Eric Doehne

Abstract: Petra, Angkor, Copan, Venice, Lascaux, Easter Island�all are examples of irreplaceable cultural heritage built in stone and now slowly disappearing. This volume is a tool for conservators and conservation scientists to guide policy, practice, and research in the preservation of stone in monuments, sculpture, and archaeological sites.

Abstract: Magnesium sulfate salts have been linked to the decay of stone in the field and in laboratory experiments, but the mechanism of damage is still poorly understood. Thermomechanical analysis shows that expansion of stone contaminated with magnesium sulfate salts occurs during drying, followed by relaxation of the stress during dehydration of the precipitated salts. We applied thermogravimetric analysis and X-ray diffractometry to identify the salt phases that precipitate during drying of bulk solutions. The results show the formation of 11 different crystal phases. A novel experiment in which a plate of salt-laden stone is bonded to a glass plate is used to demonstrate the existence of crystallization pressure: warping of the composite reveals significant deformation of the stone during re-wetting of lower hydrates of magnesium sulfate. Environmental scanning electronic microscope (ESEM)/STEM experiments show that hydration of single crystals of the lower hydrates of magnesium sulfate is a through-solution crystallization process that is only visible at a small scale (~μm). It is followed by growth of the crystal prior to deliquescence. This demonstrates that crystallization pressure is the main cause of the stress induced by salt hydration. In addition, we found that drying-induced crystallization is kinetically hindered at high concentration, which we attribute to the low nucleation rate in a highly viscous magnesium sulfate solution.

Abstract: The City of Adelaide suffers from rapid damage to historic building materials due to salts, rising damp, and damp-proof course failures. Adelaide City Council has partially funded repairs to over 400 buildings in the past 15 years. To begin to examine the scope of this problem and the effectiveness of various treatments, 24 historic buildings in Adelaide were examined, with a focus on the building materials, historic interventions and current treatments applied to treat rising damp and salt decay. Analysis of 90 samples found high levels of sodium sulfate, sodium chloride and sodium nitrate in cellars, ground water and building materials, suggesting a clear example of rising damp. Samples of disintegrating masonry, depth profiles acquired by drilling, poultices and damp proof courses (DPC) were analyzed by Ion Chromatography (IC) and Environmental Scanning Electron Microscopy coupled with Energy Dispersive Spectroscopy (ESEM/EDS). Mercury Intrusion Porosimetry (MIP) and capillarity test were carried out in the building materials and DPCs showing that porous materials with high porosity, small pores and low strength are more prone to salt weathering. The City of Adelaide is a natural laboratory for comparing and analyzing different treatments of salt-laden masonry, with hundreds of treated buildings of the same age, in the same environment, and with similar building materials.

Abstract: Since its abandonment 185 years ago, the XII century Santa Maria de Bonaval Monastery located in Guadalajara (Spain) has suffered significant deterioration: first the roof was lost, followed by partial collapse of the walls, moisture infiltration and extensive loss of stone surfaces due to salt weathering. This case study is a clear example of the incompatibility of some building materials: in this case, the combination of sulphate-bearing mortars and magnesium-rich stone and mortars leading to extensive weathering by magnesium sulphate crystallization. Samples of plaster, bedding and core mortars, stone fragments and flakes, salt crust and powders were collected, as well stone samples from the historic quarries located close to the Monastery. Characterization by XRD (X-ray diffraction), ESEM-EDS (environmental scanning electron microscopy with energy dispersive X-ray spectroscopy) shows that the most important stone-type used in the structure, dolostone, is mainly affected by magnesium sulphate salts (epsomite, MgSO4 · 7H2O), although other salts as kalicinite (KHCO3) and mercallite (KHSO4) were also detected. The connected porosity and pore size distribution determined by mercury intrusion porosimetry and capillarity behaviour suggest that the core mortar could easily be dissolved and the stone, plaster and bedding mortars are able to transport infiltrating solutions, giving rise to the precipitation of magnesium sulphate in the mortar joints and over the surface of the stone. Due to their chemical incompatibility, the combination of sulphate and magnesium-bearing mortars and stone with high magnesium content appears to be problematic and should be avoided in future restoration work.

Abstract: Samples of red and black gloss from Greek Attic pottery of the late sixth to fifth centuries bc were examined using scanning electron microscopy (SEM and FIB/STEM). The focus of the study was the chemical and microstructural characterization of the red gloss that was first produced during this period. Two groupings of red gloss were revealed. One red was found to be compositionally similar to the black glosses (labelled 'LCM coral red'). The other red showed more significant chemical differences, such as higher calcium and magnesium, in comparison to the black (labelled 'HCM coral red'). The existence of two chemically distinct reds-otherwise identical in colour and texture-suggests that there was more than one source of clay available to the Attic potters for producing red.

Abstract: Magnesium sulfate salts often result from the combination of incompatible construction materials that, when combined with a source of moisture, react to form soluble salts often leading to significant damage by flaking of the stone. Several laboratory experiments were performed to reproduce surface flaking on limestone and to evaluate the effects of humidity cycling on the damage of stone by salt crystallization. Two salt solutions were used: a single salt of magnesium sulfate and a mixture of magnesium sulfate, calcium sulfate and sodium chloride. A climate chamber was used to test the hypothesis that salt damage in the stone can be readily caused by humidity fluctuations. Damage by flaking apparently took place, by formation of deliquescent salts of low RHeq, in two types of magnesian limestone cubes impregnated with the salt mixture, while the rest of the samples developed a salt crust over the surface, but no damage was observed. By combining both, field and laboratory data, a clearer understanding the different mechanisms of decay and associated weathering types under different environmental conditions can be obtained.

Abstract: The ancient Maya combined skills in organic chemistry and mineralogy to create an important technology � the first permanent organic pigment. The unique color and stability of Maya Blue can be explained by a new model where indigo dye fills the grooves present at the surface of palygorskite clay, forming a hydrogen bonded organic/inorganic complex. Existing theory assumes the dye is dispersed inside the channels of an opaque mineral. Based on data from thermal analysis, synchrotron and neutron diffraction, ESEM and chemical modelling calculations, our new concept of Maya Blue structure resolves this contradiction and suggests some novel possibilities for more durable, environmentally benign pigments.

Abstract: An Environmental STEM detector was used in the Environmental Scanning Electron Microscope to study the morphology of two types of wet lime putty and to evaluate the fiber size of the ancient pigment known as Maya blue. Environmental Scanning Electron Microscopy (ESEM) is a technique capable of imaging non-conductive materials in their natural state.[1,2] The technique provides for neutralization of electron-induced charge build-up by the ionization of water vapour in the chamber. A novel combination of a STEM (scanning transmission electron microscopy) detec- tor and a Peltier temperature controller extends the ESEM concept into a higher magnification range than was previously possible for dynamic experiments, opening up new parameter space in the VP/ESEM for new applications. The technique is limited by the 30 keV accelerating voltage of the primary ESEM beam energy; however, in practice this limitation was overcome by using relatively thin samples. Lime mortars are making a comeback in conserving historic buildings because of their compatibility with masonry, compared to overly strong cement-based mortars. To evaluate the role of particle size and shape in the performance of two common types of lime mortar, samples of lime putty was diluted, placed on a TEM grid and cooled to 1.5 C to allow the slow evaporation of water from the sample. The results of the lime putty study reveal significant particle size and shape differences between traditionally slaked lime (calcium oxide reacted with excess water to form a putty; Figure 1) and lime hydrate (modern, dry powdered calcium hydroxide with added water). While both contain apparently amorphous spherical particles in the size range of 0.1 to 1 micron, the traditional lime putty contains fine needle-shaped crystals of calcium hydroxide (~0.2 microns diameter), while the modern lime contains larger, more irregular shaped grains (~0.5�2 microns). These particle differences may account for observed differences in the bulk behavior of the two types of lime.[3] The greater resolution of the STEM mode and the fine control of water condensation and evaporation through the Peltier device enabled a clearer understanding and record of the evolution of lime particle size and shape. STEM-ESEM analysis of particles of Maya blue pigment�a complex of indigo dye and palygorskite clay�unexpectedly revealed that the clay fibers seen in gold-coated SEM samples are actually bundles of smaller fibers on the order of 10�100 nm in diameter easily seen in STEM images (Figure 2). The Environmental STEM detector will likely be applied to a wide range of problems, from bio-medical to materials science applications.[4] FIG. 1 Environmental STEM image of slaked lime putty. Note needles of calcium hydroxide. FIG. 2 STEM image of Maya blue clay fibers. Note 300,000X magnification. References 1. Do Amaral M, Bogner A, Gauthier C, Thollet G, Jouneau P-H, Cavaille J-Y, Asua JM: Novel experimental technique for the de- termination of monomer droplet size distribution in miniemulsion. Macromolec Rapid Comm 26, 5, 365�368 (2005) 2. Doehne E: ESEM development and application in cultural her- itage conservation. In In-Situ Microscopy in Materials Research (Eds. Gai P). Kluwer Academic Publishers, Dordrecht, (1997) 45�62 3. Doehne E, Stulik DC: Applications of the environmental scanning electron microscope to conservation science. Scan Microsc 4, 2, 275�286 (1990) 4. Rodriguez-Navarro C, Hansen E, Ginell W.S: Calcium hydroxide crystal evolution upon aging of lime putty. J Amer Cer Soc 81, 11, 3032�3034 (1998)

Abstract: The application of ESEM technology to the conservation of cultural heritage and other fields is reviewed. Several applications are presented with a focus on reaction kinetics and micro to nano-scale material behaviours, including time-lapse studies of reaction kinetics for NaCl and NaNO3; verification of the stone decay mechanism at the site of Copan, Honduras; and ESEM/EDS analysis of the first photograph (1826). A review of other ESEM applications reveals some important trends, especially in the materials science, electronics and biosciences fields, such as quantitative ESEM/EDS; 1.8�nm resolution imaging of extreme insulators in VP/ESEM; and ESEM analysis of emulsions and cells.

Abstract: While the Environmental Scanning Electron Microscope (ESEM) allows high-resolution characterization of material surfaces in their natural state, access to data in the third dimension is often necessary to realistically evaluate the condition of dynamic systems, such as the weathering processes affecting monuments and sculpture. Data presented here show that X-ray Microtomography (CT [1] and micro-CT) can provide an important supplement to ESEM/EDS microanalysis when studying the deterioration of stone by the sub-surface crystallization of magnesium sulfate salts. Magnesium limestone is widely used in historic architecture and monuments, especially in the north of England. York Minster, the largest gothic cathedral in Northern Europe, is also located near one of Europe�s largest coal fired powerplants. Magnesium sulfate salts, produced by the reaction between the stone and airborne sulfate tend to accumulate in sheltered areas and crystallize episodically beneath the stone surface. This crystallization reaction was studied using oolitic limestone test blocks and saturated magnesium sulfate solution setup in the laboratory so that continuous crystallization would occur from a reservoir [Fig. 1]. CT data was acquired using a standard 450 kV Philips industrial X-radiography setup modified with a new detector comprised of a mirror, Apogee high resolution camera, and cesium iodide scintillator screen along with software developed by Dr. Pasini and the University of Bologna. The preliminary results of the study show that the crystallization takes place in a zone parallel to the stone surface that appears to leave the stone interior largely intact. ESEM results show two morphological types of salt crystals: anhedral at the stone/salt interface and columnar as the salt separates the stone layer from the stone core. CT results show several distinct density zones, which appear to correspond to the degree of disruption of the stone [Fig. 2]. References [1] V.G. Mossotti and L.M. Castanier, The measurement of water transport in Salem limestone by x- ray computer aided tomography, in International symposium on The engineering geology of ancient works, monuments and historical sites; preservation and protection, P.G. Marinos and G.C. Koukis, Editors. 1990, Balkema: Rotterdam. p. 2079-2082. [2] Acknowledgements: The support of Dr. Giacomo Chiari and Dr. Franco Casali in this research is gratefully acknowledged.

Abstract: The Hieroglyphic Stairway at Copan in Northwest Honduras is the longest inscription known from the Ancient Maya. As part of a larger conservation project of the Institute Hondurenio de Antropologia e Historia (IHAH) and the Getty Conservation Institute (GCI), blocks of uncarved green and buff volcanic tuff as well as samples of flaking tuff from the Hieroglyphic Stairway, were characterized for their material properties and state of decay. Flaking appears to be connected to selective dissolution, hygric cycling, lichen hyphae and calcite precipitation in stone fractures. These results represent the first comprehensive characterization of these materials and aid the understanding of material durability, behavior and conservation for this important site.

Abstract: For EDS �spot� analyses in the ESEM, data presented here show that two subtraction methods using internal standards can provide a useful indication of what elements are truly present in the sample under the primary beam and what portion of the signal is actually part of the ancillary X-ray spectrum produced by gas-scattered electrons. The increasing popularity of ESEM, VP-SEM, and LV-SEM instruments has raised interest in ways to differentiate or unmix these two X-ray signals generated in these instruments. Under conditions of high gas pressure or long gas path length, a significant fraction of the electrons that make up the primary beam are scattered after colliding with gas molecules as the beam passes through the higher- pressure region above the sample. These electrons form a broad, flat skirt that surrounds the primary beam [1, 2]. Previous experiments have documented the shape of the skirt and its effect on the X-ray resolution [3, 4]. Efforts to establish quantitative correction methods for EDS microanalysis to account for the effect of skirt X-ray events have been successful [5-7], but somewhat cumbersome and time-consuming. A more popular approach for spot analyses has been to minimize skirt formation through the use of lower gas pressures and shorter gas path lengths where possible and the invention of extended detectors optimized for ESEM/EDS, which move the vacuum closer to the sample [8, 9]. Nevertheless, there are situations where a significant X-ray skirt component is present, for example, in instruments with a normally long gas path length (VPSEM and LVSEM) and in the microanalysis of hydrated materials (ESEM). For qualitative analysis, often what is required is a rapid indication of what elements in the �mixed� spectra are truly under the primary beam and what part of the overall spectra is coming from the skirt. Data presented here evaluate the effectiveness of simple subtraction methods to unmix the spectra. Two approaches were tested: one where the beam is fixed and the pressure is varied. The two spectra are subtracted to obtain a skirt spectrum. The skirt spectrum can then be used to evaluate the �purity� of the initial, mixed spectrum. The second method is one where the beam is rapidly scanned over the skirt area to acquire a simulated skirt spectrum which is then subtracted from a �spot spectrum� to produce a �skirt� spectrum. Each method has been proposed [10, 11], but additional testing is needed to verify the limits and speed of the methods. We also suggest the use of an internal standard in the skirt area to act as a guide to the degree of subtraction required and an evaluation of the time required to determine if an element is truly in the skirt or under the beam (Figs. 1 & 2). Any element that is only present in the skirt area will function as an internal standard. Copper tape works well in this case. References [1] D.A. Moncrieff, P.R. Barker, and V.N.E. Robinson, J. Phys. D: Appl. Phys., 1979. 12: p. 481- 488.Microsc Microanal 11(Suppl 2), 2005 31 [2] G.D. Danilatos, Advances in Electronics and Electron Physics, 1988. 71: p. 109-250. [3] E. Doehne and N. Bower, Microbeam Analysis, 1993. 2(supplement): p. S35-36. [4] B.J. Griffin, R.L. Trautman, and J. Coffey. MAS'93: Microbeam Analysis Society 27th Annual Meeting and AEM. 1993. Los Angeles, CA (USA). [5] E. Doehne, Scanning, 1997. 19(2): p. 75-78. [6] R. Gauvin, Scanning, 1999. 21(6): p. 388-393. [7] J.B. Bilde-Sørensen, Microscopy Today. 1998. p. 10. [8] N.W. Bower, D.C. Stulik, and E. Doehne, Fresenius Journal Analytical Chemistry, 1994. 348(5- 6): p. 402-410. [9] T. Rice. 2002. Personal Communication. [10] R.B. Bolon. Microbeam Analysis 1991, the 25th Annual Conference of the Microbeam Analysis Society. 1991. San Jose, CA: San Francisco Press, Inc., Box 6800, San Francisco, CA 94142-6800. USA 1991. [11] E. Doehne, Scanning, 1996. 18(3): p. 164-165. [12] Acknowledgements: The support of Giacomo Chiari and David Carson in this research is gratefully acknowledged. Stimulating discussions with colleagues Robert Carlton and Brendan Griffin have helped to further develop the ideas presented here. FIG 1. EDS Spectra showing A) original mixed spectrum showing Cu (internal standard) and complex aluminosilicate B) subtraction to produce �skirt� spectrum containing Cu and K not present in area under the primary beam C) final corrected spectrum with pressure change method [5]. Fig 2. Backscattered electron image of volcanic tuff showing several phases. For qualitative spot analysis an internal Cu standard is used to control the degree of empirical correction required. 320μm width.

Abstract: Natural purple pigments are extremely rare. Between 479 BC and 220 AD, a new pigment known as Han Purple was manufactured in China [1]. To aid in the reproduction of this ancient technology, quantitative phase analysis of an octagonal Han Purple color stick was carried out using the electron microprobe. The purple in Han Purple is a Barium Copper Silicate (BaCuSi2O6) related to Egyptian Blue, a Calcium Copper Silicate pigment first manufactured in 3000 BC (CaCuSi4O10) [1]. Han Purple is also related to the production of Han Blue, a similar Barium Copper Silicate (BaCuSi4O10) [2, 3]. All three of these pigments are produced in a manner that often results in complex frits, consisting of several mineral phases and a glass matrix. Han Purple appears to have been created primarily using mineral components (barite for barium, malachite and azurite for copper and quartz sand for silica), fired at about 1000 C. The complete recipe for Han Purple is not yet understood. One of the uses of this pigment was to decorate elements of the well-known Terracotta Army of Northern China, in Xi�an. A transition between the darker and lighter areas of the purple pigment stick (Fig. 1) was found to be due to leaching of glass, as shown by the loss of sodium (Fig. 2). The surface layer largely contains elements that appear to have been leached from the glass. The results help in determining the starting materials for this complex material, which was unexpectedly found to be rich in lead (see Table 1). This work suggests that the unexpectedly lead-rich glass associated with the manufacture of Han Purple may provide important information on the starting materials for this complex ceramic as well as potential evidence concerning the melting temperature of the frit [4]. References [1] S. Bouherour, H. Berke, H.-G. Wiedemann, Chimia 2001, 55, 942�951. [2] J. Riederer, Egyptian Blue, in Artists' Pigments: A Handbook of Their History and Characteristics - Volume 3, ed. by E. W. Fitzhugh, National Gallery of Art, Washington, 1998. [3] D. A. Scott, Copper and Bronze in Art: Corrosion, Colorants, and Conservation, Getty Conservation Institute, Los Angeles, 2002. [4] The advice of Dr. David Scott of UCLA and Dr. Dale Newbury of NIST is gratefully acknowledged.

Abstract: Having a controlled environmental chamber with in situ high resolution imaging (i.e. ESEM), has advanced our understanding of important dynamic processes such as corrosion and dissolution/crystallization [1, 2]. However, in order to further advance into the important area of reaction kinetics it is important to begin to better quantify the environment in the chamber, as well as some of the limits of dynamic experiments using the ESEM. Typical questions that need to be addressed: Are the humidity cycles in the ESEM reproducible? Are there temperature offsets between the thermocouple and different sample stubs? Between the stub and the top of a millimeter-scale crystal? What is the profile of the temperature gradient between the gas at ambient temperature and a cooled sample? How long does it take for the environment in the ESEM chamber to stabilize at the beginning of a run? At what beam dose does the heat and radiation from the electron beam significantly influence the reaction being observed? Since it is not possible to see through thick water layers in ESEM, how do you assess if full dissolution of a solid has occurred during a dissolution/crystallization cycle? Using the well-known deliquescence and crystallization behavior of NaCl [3], this work begins to address such questions. The crystallization of small salt particles is important for many reasons: to atmospheric scientists interested in the behavior of sea-salt aerosol particles (1012 kg/yr), for cement chemists studying chloride penetration and rusting rebar in our deteriorating infrastructure, in the food industry, and to conservation scientists interested in salt weathering of building materials from crystallization pressure [4, 5]. NaCl deliquesces and crystallizes at about 75% RH over a wide range of temperature allowing it to be used to help calibrate the ESEM environment. A series of dynamic experiments using NaCl have been performed using an Environmental Scanning Electron Microscope (ESEM, FEI XL30/FEG) with standard Peltier heating and cooling stage. By changing the RH% in the chamber it is possible to document the development of phenomena such as adsorption/desorption and dissolution/crystallization of the NaCl crystals. The ambient temperature in the ESEM chamber is about 26 C while the temperature of the sample is adjusted through the use of the Peltier stage [6]. RH% is modified by changing the pressure through a computer-stabilized needle valve; while sample temperature is keep constant by the means of a Peltier stage [4]. The pressure variations are instantaneous and easily recorded, for instance at 10°C a 13 Pascal pressure variation is obtained in a fraction of a second and corresponds to a 1% RH change (calculated value). Temperature variations are controlled via software and the Peltier stage and require a longer time to adjust to the set-up value, generally 15-30 minutes to attain the specified conditions. NaCl deliquesces at 75% RH at 20 C and this is used to calibrate the ESEM chamber environment. A temperature offset (dT) has been observed between the setup and the actual value (Fig. 1a & 1b) especially below 10°C. The dT varies from 0 to 1°C depending on the stub morphology for the constitutive material (steel, aluminium). The temperature offset is taken into account for the RH% determinations reported here. The experiments have also demonstrated that there is no noticeable offset between the surface temperature of the stub and the upper surface of the salt crystal in the investigated range (crystal diameter from few microns up to 1 mm). As expected, absorption/dissolution of NaCl is generally more rapid than desorption/crystallization. Also, crystal size plays a key role in the kinetics of dissolution. For example, a 100 μm NaCl crystal is observed to dissolve 2-3 times faster than a 250 μm crystal [7]. References [1] E. Doehne and D. Stulik (1991). Dynamic studies of materials using the environmental scanning electron microscope, Materials Research Society Proc. 187: 23-29, Pittsburgh. [2] E. Doehne (1997). ESEM development and application in cultural heritage conservation. In- Situ Microscopy in Materials Research. P. Gai. Dordrecht, Kluwer Academic Publishers: 45-62. [3] D. W. Kaufmann, Sodium Chloride: The Production and Properties of Salt and Brine. New York: Hafner Publishing Company, 1971. [4] E. Doehne, (1994). In situ dynamics of sodium sulfate hydration and dehydration in stone pores: Observations at high magnification using the environmental scanning electron micro- scope. The conservation of monuments in the Mediterranean Basin III, Venice, Italy, Soprin- tendenza ai Beni Artistici e Storici di Venezia. [5] E. Doehne, (2002). Salt weathering: a selective review. Geological Society Special Publication 205: Natural Stone, Weathering Phenomena, Conservation Strategies and Case Studies: 51-64. [6] Cameron, R. E. and A. M. Donald (1994). Minimizing sample evaporation in the environmental scanning electron microscope. Journal of Microscopy 173(3): 227. [7] The advice of Stefan Simon and Ralph Knowles is gratefully acknowledged.

Abstract: Incorporating the results of a meeting held in London in 2000, sponsored by English Heritage and the Getty Conservation Institute, this article reviews both consolidants and protective treatments for the conservation of deteriorated limestone and lime plaster. Carbonate deposition (including both inorganic solutions and biomineralization), barium hydroxide treatment, ammonium oxalate and tartaric acid treatments are covered. The article reviews selected literature, identifies open questions and promotes discussion of a range of issues, encompassing application techniques, performance, compatibility and retreatability. While many questions concerning these important systems have been addressed in published sources, there are significant opportunities for new research.

Abstract: The effects of [Fe(CN)(6)](4-) ions on the crystallization of NaCl in aqueous solution has been studied, particularly in the situation where the saline fluid percolates through and evaporates from a saturated porous body (i.e., an ornamental porous limestone). In concentrations ranging from 2.48 x 10(-4) Up to 2.85 10(-3) M the additive was able to increase the solution critical supersaturation (up to 8%) resulting in a significant crystallization inhibition effect, which promoted efflorescence growth on the porous stone surface as opposed to subflorescence growth. The former induced no damage to the stone support while the latter always resulted in crystallization pressure development inside the pores, causing granular disintegration-a process also known as "salt weathering". Significant changes in NaCl crystal growth morphology (from {0 0 1} towards {1 1 0}, {1 1 1} and {2 1 0} forms) were observed in the presence of ferrocyanide ions, which also promoted the growth of dendrites with their main growth axis parallel to <1 1 1>, and branched along <1 0 0>, at the highest supersaturation. The possible inhibiting mechanism of ferrocyanide on NaCl crystallization and growth is discussed based on the evolution of NaCl growth morphologies, and some practical applications of ferrocyanides to prevent salt damage and enhance desalination in ornamental stones are outlined. (C) 2002 Published by Elsevier Science B.V.

Abstract: Crystallization modifiers can significantly affect the capillary passage of dilute and concentrated solutions of sodium chloride and sodium sulfate through columns of limestone. In the absence of modifiers, sodium chloride passage through Monks Park limestone gave predominantly subflorescence with mild edge erosion while sodium sulfate mainly effloresced and severely damaged the stone column. With Texas Creme limestone, a stone of moderately higher porosity, essentially only efflorescence occurred with either salt and there was little or no stone damage. Uniquely, alkali ferrocyanides were found to impact significantly on the interaction of these solutions as they moved through the limestone. The addition of 0.10-1.00% of K4Fe(CN)(6) to sodium chloride in Monks Park limestone experiments increased the flow rate of solutions through the stone, resulting in efflorescence in place of subflorescence, and yielded a massive formation of extended dendritic filaments without damaging the stone. This protection by additive was extended to sodium sulfate solutions, but only at lower salt concentrations. Results comparable to the effect of adding K4Fe(CN)(6) to concentrated sodium chloride Monks Park limestone experiments were obtained with saturated sodium sulfate solutions without additives by conducting the experiments in a draft-free, high humidity environment--suggesting a potentially useful strategy for the conservation of fragile, salt-laden objects. These results are explained by factors causing evaporation of solution to occur either below or at the surface of the stone, and by the effect of modifiers on the crystal habit of the salts forming during evaporation in this region.

Abstract: Charge contrast imaging (CCI) is a useful new method for imaging sub-micron features in crystalline materials using the unique gas/ion/electron imaging system of the environmental scanning electron microscope (Griffin, 1997; Doehne, 1998). Crystal growth zoning, microfractures, solution boundaries, and areas of chemical alteration or recrystallization can be imaged in a wide range of materials (Griffin, 2000; Watt, et al. 2000). While not fully understood, charge contrast images reflect differences in the ability of materials to accept, store and discharge deposited electrons from the primary electron beam. These differences are expressed, in turn, as contrasts in secondary electron emission from flat samples (e.g. these contrasts are not related to topography, as is usually the case). Charge contrast appears be related to differences in electronic properties which are often controlled by defect density. CCI is also affected by small-scale physical defects (such as microfractures) which appear to affect the distribution and timing of charge buildup and discharge in the sample (Johansen, et al. 1997). It is not clear if charge contrast is due to differences in the number, energy distribution or depth of the secondary electrons being emitted, or some combination. The remarkable 3-D appearance of the CCI images obtained from flat samples is worth noting and suggests a potential dependence of this contrast on secondary electron escape depth. CCI has also been called charge-induced contrast (Harker 1994) while earlier authors have suggested the term impurity-sensitive contrast (Sawyer and Page 1978). To further develop this method, we present here data on the variation of CCI contrast with typical ESEM instrument parameters. Charge contrast imaging was first noted by the authors when studying samples of Travertine stone from Tivoli, Italy, which consists mostly of calcite. The conditions in the ESEM were systematically varied and the impact on the CCI contrast noted. The average trends from a series of these tests are summarized in Figure 1. A typical sample is illustrated in Figures 2 and 3. The contrast observed in the calcite sample appears primarily as darker and lighter, often parallel bands (crystal growth banding), complex, symmetrical features (which resemble sector zoning) and irregular interfaces (apparently dissolution surfaces). Cathodoluminescence (CL) images of calcite are similar to CCI images, but much less detailed. CCI contrast in our calcite sample appears to occur under conditions of high detector gain (detector bias or electronic gain) and fast scan rate (Figure 1). Obtaining high contrast CCI images at short working distance was not possible due to arcing from the detector to the sample with a high detector bias. Somewhat longer working distances allowed the detector bias to be put to the maximum on this instrument (~535 volts). The greatest CCI contrast appears at the highest kV with decreasing contrast visible in some areas until about 5 kV. Future work on this useful method will extend to other types of carbonate samples. References Doehne, E.: Charge contrast: some ESEM observations of a new/old phenomena. In G.W. Baily, Ed., Microscopy and Microanalysis 1997, 4 (Supplement 2), 292-293, Springer, Atlanta, Georgia. (1998). Griffin, B. J. Charge contrast imaging of material growth and defects in the environmental scanning electron microscopy � Linking electron emission and cathodoluminescence. Scanning 22:234-242 (2000). Griffin, B. J.: A new mechanism for the imaging of crystal structure in non-conductive materials: An application of charge-induced contrast in the environmental scanning electron microscope (ESEM). In G.W. Baily, et al, Eds., Microscopy and Microanalysis 1996, 3, (Supplement 2), 1197-1198 (1997). Harker, A. B., D. G. Howitt, J. F. DeNatale, and J. F. Flintoff: Charge-sensitive secondary electron imaging of diamond microstructures. Scanning, 16, 87-90 (1994). Johansen, H., Erfurth, W. Gogoll, S., Stenzel, E., Reichling, M., and E. Matthias: Scanning electron microscopy imaging of microcracks and charging phenomena on a laser-damaged CaF2 surface. Scanning, 19, 416-425 (1997). Sawyer, G. R. and T.F. Page: Microstructural characterization of 'REFEL' reaction bonded silicon carbide. Journal of Materials Science. 13, 885-904 (1978). Watt, G. R., Griffin, B.J., Kinny, P.D.: Charge contrast imaging of geological materials in the environmental scanning electron microscope. American Mineralogist, 85:1784-1794 (2000).

Abstract:

Abstract: The fundamental behavior of sodium sulfate crystn. and induced decay in concrete and other building materials is still poorly understood, resulting in some misinterpretation and controversy. We exptl. show that under real world conditions, both thenardite (Na2SO4) and mirabilite (Na2SO4.cntdot.10H2O) ppt. directly from a satd. sodium sulfate soln. at room temp. (20.degree.C). With decreasing relative humidity (RH) and increasing evapn. rate, the relative proportion of thenardite increases, with thenardite being the most abundant phase when pptn. occurs at low RH in a porous material. However, thenardite is not expected to crystallize from a soln. at T<32.4.degree.C under equil. conditions. Non-equil. crystn. of thenardite at temps. below 32.4.degree.C occurs due to heterogeneous nucleation on a defect-rich support (i.e., most porous materials). Anhyd. sodium sulfate pptn. is promoted in micropores due to water activity redn. Fast evapn. (due to low RH conditions) and the high degree of soln. supersatn. reached in micropores before thenardite pptn. result in high crystn. pressure generation and greater damage to porous materials than mirabilite, which crystallizes at lower supersatn. ratios and generally as efflorescence. Data from the environmental scanning electron microscope (ESEM) show no hydration phenomena following wetting of thenardite; instead, thenardite dissoln. occurs, followed by thenardite plus mirabilite crystn. upon drying. These results offer new insight into how damage is caused by sodium sulfate in natural geol., archaeol., construction and engineering contexts. They also help explain some of the controversial results of various commonly used sodium sulfate crystn. tests.

Abstract: The interactions of two ionic surfactants on the decay of ornamental stone (porous limestone) by salt crystallization, a common and damaging weathering process, were studied. Conductivity and/or surface tension measurements allowed calculations of the critical micellar concentration (cmc) of sodium dodecyl sulfate (SDS) and cetyldimethylbenzylammonium chloride (CDBAC) in distilled water and saturated sodium sulfate solution (both with and without the addition of calcite), total surfactant adsorption onto calcite (?tot), and the area (As) which a surfactant molecule occupies at the liquid-air interface. In aqueous calcite suspensions SDS shows a strong cmc reduction due to Ca2+ binding to the micelles that undergo sphere-to-rod transition at SDS concentrations > cmc, while calcium dodecyl sulfate (Ca(DS)2) precipitation contributes to a reduction of DS- concentration in the bulk solution. Adsorption of DS- on calcite is promoted in the saturated saline solution where ?tot reaches values of 1 � 10-2 mmol m-2. CDBA+ is preferentially adsorbed onto calcite in water (?tot = 1.89 � 10-3 mmol m-2) while adsorption on calcite in saturated sodium sulfate solution is limited (?tot = 2.18 � 10-4 mmol m-2) due to competition with Na+ for calcite adsorption sites. Limited CDBA+ adsorption onto calcite, and significant As reduction in the saline solution, results in sphere-to-rod (or disk) micelle shape transition. The previous results together with in situ, high magnification environmental scanning electron microscopy (ESEM) studies and macroscale salt crystallization tests revealed that: (a) the adsorption behavior of DS- induces crystallization of mirabilite at high supersaturation, resulting in nonequilibrium crystal shapes that promote significant damage to the stone; (b) rodlike and/or disc-shaped CDBA+ micelles enhance solute solubilization and transport to mirabilite nuclei growth sites, inducing crystallization of euhedral crystals formed at low supersaturation and distributed homogeneously throughout the stone pore system. While CDBAC initially reduces stone damage by salt crystallization, it can ultimately result in enhanced damage when in contact with water due to mechanical weakening of the stone and rehydration of previously dehydrated mirabilite crystals within the stone pores. The implications of these results in the conservation of ornamental stone are discussed.

Abstract: Honeycomb weathering is a common surface phenomenon affecting a variety of rocks in a range of environments. It develops on building stones and it shapes ocean cliffs, rocks in hot deserts, and Arctic landscapes. Honeycomb weathering may also help alter rocks on other planets, such as Mars. Although first noted in the nineteenth century, its origins are still not well understood, and a dearth of laboratory experiments testing the many theories proposed for its development has added to the ambiguity. Incipient honeycomb weathering in a homogeneous limestone has been experimentally reproduced by wind exposure and salt crystallization. Our experiments show that heterogeneous wind flow over a stone surface is important in the development of this weathering pattern. Wind promotes evaporative salt growth between grains on a stone surface, resulting in the development of small, randomly distributed cavities. A reduction in air pressure within the cavities results in increased wind speed and rapid evaporation. A high evaporation rate and evaporative cooling of the saline solution in the cavity leads to more rapid and greater granular disintegration than in the surrounding areas. It seems that this local supersaturation and subsequent buildup of salt crystallization pressure ultimately result in the formation of honeycomb features. For the first time, these experimental results demonstrate the close relationship between salts, wind, and honeycomb weathering. They also offer new ways to understand the genesis of this striking and sometimes harmful weathering pattern.

Abstract: In situ visual analysis in heritage conservation is important for understanding time-dependent processes such as weathering of stone and other building materials. This paper describes the application of time-lapse video microscopy coupled with scanning electron microscopy for this purpose. A challenging analytical problem in the field of heritage conservation is the need for in-situ visual analysis and understanding of time-dependent processes such as the weathering of stone and other building materials. This type of information is critical, but rare, since the tools for such a task and the ability to integrate them economically have only recently become available. Nevertheless, dynamic information acquired on the nanometer to centimeter scale is critical to our understanding the evolution of these processes and how the dam- age caused by weathering varies with key environmental parameters. This, in turn, constrains our ability to conserve monuments: from the Sphinx in Egypt to the endangered Buddhist caves along the Silk Road. Ideally, this information should be collected in situ on the site; however, laboratory studies using the appropriate technology have proven to be useful in studying model systems.

Abstract: Micro- and macroscale expts. which document the dynamics of salt damage to porous stone have yielded data which expose weaknesses in earlier interpretations. Previously unexplained differences are found in crystal morphol., crystn. patterns, kinetics and substrate damage when comparing the growth of mirabilite (Na2SO4. 10H2O) and thenardite (Na2SO4) vs. halite (NaCl). The crystn. pattern of sodium sulfate was strongly affected by relative humidity (RH), while a lesser RH effect was obsd. for sodium chloride. Macroscale expts. on oolitic limestone confirmed that mirabilite (crystg. at RH > 50 per cent) and thenardite (crystg. at RH < 50 per cent) tend to form subflorescence in highly localized areas under conditions of const. RH and temp. This crystn. pattern was more damaging than that of halite, since halite tended to grow as efflorescence or by filling the smallest pores of the stone in a homogeneous fashion, a result which contradicts the theor. model of salt damage of Wellman and Wilson (1965). Low RH promoted rapid evapn. of saline solns. and higher supersatn. levels, resulting in the greatest damage to the stone in the case of both sodium sulfate and sodium chloride crystn. At any particular crystn. condition, sodium chloride tended to reach lower supersatn. levels (resulting in the crystn. of isometric crystals) and created negligible damage, while sodium sulfate reached higher supersatn. ratios (resulting in non-equil. crystal shapes), resulting in significant damage. Environmental SEM showed no damage from sodium sulfate due to hydration. Instead, after water condensation on thenardite crystals, rapid dissoln. followed by pptn. of mirabilite took place, resulting in stone damage by means of crystn. pressure generation. It is concluded that salt damage due to crystn. pressure appears to be largely a function of soln. supersatn. ratio and location of crystn. These key factors are related to soln. properties and evapn. rates, which are constrained by soln. compn., environmental conditions, substrate properties, and salt crystn. growth patterns. When combined with a crit. review of salt damage literature, these expts. allow the development of a model which explains variations in damage related to combinations of different salts, substrates and environmental conditions.

Abstract: An ancient Egyptian limestone sculpture was found to be undergoing major structural decay when stored in a museum environment. Mineralogical and petrographic analysis of the limestone showed a high proportion of clay (> or =10% by weight) that was concentrated along bedding planes. The clay fraction consisted mostly of sepiolite (>90%) and palygorskite (<10%). Minor quantities (< or =1%) of soluble salts (NaCl and NaNO 3 ) were also found. Wetting/drying with distilled water and relative humidity cycling resulted in the same delamination cracking damage as that observed in the museum environment. Thermomechanical analyses (TMA) confirmed that the damage was due to expansion (>4.5%) parallel to bedding planes when the limestone was immersed in water. The expansion due to swelling of the clays was directly observed at high magnification in an environmental scanning electron microscope (ESEM) when wetting/drying cycles were performed. X-ray diffraction (XRD) analysis showed that crystalline swelling of sepiolite occurred. This was determined by a shift of (110) reflection (from 12.07 to 12.20 Aa) and a decrease of (060) reflection (4.47 Aa, to 4.44 and 4.41 Aa), when in contact with ethylene glycol (EG) and dimethyl sulfoxide (DMSO), respectively. Swelling also occurred due to hydration of the clay surfaces and to electrostatic forces between clay particles, which, it was assumed, was promoted by the presence of Na counterions in water solution. Possible treatments for the conservation of these artistic objects are proposed and discussed.

Abstract: Over the past few years there have been occasional reports of unusual secondary electron contrasts in certain nonmetallic materials using conventional (CSEM�Johansen et al, 1997), low voltage (LV-SEM�Harker et al, 1993; Harker et al, 1994) and environmental scanning electron microscopy (ESEM�Griffin, 1997; T. Hardt, personal communication) which have documented novel contrast mechanisms whose origins are not yet well understood. Indeed, similar observations were made over 20 years ago in certain uncoated materials (such as SiC) using conventional SEM (Sawyer and Page, 1978). Typically, these �odd� contrasts reveal previously unavailable information (i.e. growth banding), with high spatial resolution. Aspects of these charge contrast imaging (CCI) phenomena are further documented here in a series of ESEM experiments on polished cross sections of uncoated calcite. What is �old� is the fact that these contrasts have been reported on several occasions. What is �new� is the observation that these unusual contrasts are more readily studied and, in some cases, have been found in a wider range of materials using ESEM. The results of this paper suggest that one of these new/old electron contrasts (CCI-1) appears to be correlated with the degree of order in the calcite lattice and under certain conditions is dependent on the charge decay time (the contrast actually increases with increasing scan speed). CCI-1 images are similar to CL contrasts produced by variations in trace element distributions or density of growth defects. The exact mechanism of contrast formation is not clear, but is thought to be related to variations in defect trapping states, band gap energy and the depth of secondary electron emission. We speculate that changes in the secondary electron (SE) emission depth may be responsible for the remarkable 3-D appearance of the CCI-1 contrast. A second contrast phenomena (CCI-2) appears to be caused by accumulated subsurface charge leading to enhanced surface electron emission and the suppression of other contrasts. The presence of the positive ion flux in the ESEM makes it possible to image and study this phenomena in some detail. The time-dependent nature of both charge contrasts suggests some useful imaging possibilities. Further study is warranted of these intriguing new/old contrast mechanisms, which are part of a whole class of time-resolved phenomena in scanning electron microscopy (TR-SEM).

Abstract: ESEM and Video Microscopy Studies in Stone Conservation Eric Doehne The Getty Conservation Institute, Los Angeles, California, USA Observation of stone deterioration using in situ, time-lapse microscopy techniques has revealed previously undescribed material behaviors that help to explain the destructive effects of several, important processes in wall paintings, historic structures and monuments. It has long been. acknowledged that cyclic stresses imparted by humidity changes, wet-dry cycling, and the crystallization and hydration of soluble salts, are important agents in the deterioration of these porous structures. The crystallization of salts is a particularly serious conservation problem (Arnold, 1975). Over time, cyclic salt crystallization results in the physical breakdown of the material (Goudie, 1993). Objects affected by such processes are often difficult to conserve since they are weak to begin with and the presence of salt inhibits the curing of some common conservation materials (Price and Kumar, 1994). Sodium sulfate is one of the most damaging of salts, apparently because it expands during the transition from the anhydrous phase (Na2S04; thenardite) to the decahydrate form (Na2S04_l0H2O; mirabilite). This transition may occur with changes in temperature or relative humidity. Sodium chloride (halite) is also commonly associated with damage to stone. While the correlation between extensive damage and the presence of salts is clear (Goudie, 1993) the exact mechanisms of deterioration are still debated (McMahon and others, 1992). A series of experiments were performed to document the dynamic behavior of. sodium sulfate and sodium chloride during hydration, dehydration, dissolution and crystallization cycles at magnifications of 10x-10,000x using video microscopy and the environmental SEM. The ESEM makes the observation of small-scale dynamic processes at high water vapor pressures possible, without sample coating or other pretreatment (Doehne and Stulik, 1990).

Abstract: Spurious x-ray signals, which previously prevented high-resolution energy-dispersive x-ray analysis (EDS) in the environmental scanning electron microscope (ESEM), can be corrected using a simple method presented here. As the primary electron beam travels through the gas in the ESEM chamber, a significant fraction of the primary electrons is scattered during collisions with gas molecules. These scattered electrons form a broad skirt that surrounds the primary electron beam as it impacts the sample. The correction method assumes that changes in the width of the electron skirt with pressure are less important than changes in the skirt intensity; this method works as follows: The influence of the gas on the overall x-ray data is determined by acquiring EDS spectra at two pressures. Subtracting the two spectra provides us with a difference spectrum which is then used to correct the original data, using extrapolation, back to the x-ray spectrum expected under high-vacuum conditions. Low-noise data are required to resolve small spectral peaks; however, the principle should apply equally to x-ray maps and even to low-magnification images.

Abstract: An intriguing problem in environmental microscopy is the seemingly impossible task of performing spatially resolved quantitative energy-dispersive spectroscopy (EDS) analysis and high-resolution x-ray mapping under humid conditions (i.e., >50% RH; see diagram in Messier and Vitale 1993). A new method presented here largely overcomes these problems by correcting for the contribution of x-rays generated by scattered electrons. Under humid conditions in the environmental scanning electron microscope (ESEM), a large fraction of the electrons that make up the primary beam are scattered after colliding with gas molecules as the beam passes through the high pressure region above the sample. These electrons form a broad skirt which surrounds the primary beam (Danilatos 1988). Previous experiments have documented the shape of the skirt and its effect on the x-ray resolution (Doehne and Bower 1993, Griffin et al. 1993). Other workers have found through empirical studies that adequate EDS maps and spot analyses can be obtained by significantly lowering the chamber pres- sure and moving the vacuum closer to the sample using extended bullets (Bower et al. 1994, T. Hardt, personal communication). However, these methods do not provide a solu- tion for those users who require EDS analysis with adequate x-ray resolution under humid conditions. The analysis of hydrated biological materials is an obvious example. A correction method has been developed which appears to compensate effectively for the x-rays generated by the electron skirt and which functions to preserve the x-ray signal generated by the primary beam. The method is as follows: An x-ray spectrum (A) or map is acquired under conditions of high chamber pressure (8 Torr, for example). Another measurement (B) is made under identical conditions, but at a lower chamber pres- sure (4 Torr). The difference between the two spectra provides information on how decreasing the contribution of the x-rays generated by the skirt electrons affects the overall spectrum. If C is the spectrum at zero Torr (no skirt effect), then we can approximate C by the following: C � B � [(A � B) * D]. This simple equation assumes that A is acquired at twice the chamber pressure as B. The method also assumes that changes in the lateral extent of the x-ray skirt are less important than changes in the skirt intensity (see Doehne and Bower 1993). D is an empirical factor derived from observing when the x-ray background shape of spectrum B is significantly altered by the subtraction of the spectral differences between A and B. The background shape acts as a built-in check against overcorrec- tion. If the difference in a particular channel between spectrum A and B is negative, then further reducing the intensity of that channel by an empirical factor (D) will result in a spectrum similar to C. In other words, as the skirt intensity is reduced, the x-ray contribution for a particular element may increase or decrease in rough proportion to whether that element is present mainly in the skirt area or in the area analyzed by the primary beam. If the channel intensity does not change as the pressure is changed, we can then assume that the skirt and primary com- positions are similar for that channel. Further development and testing of this method is currently underway with promising preliminary results (Fig. 1). While this new skirt correction pro- cedure has double the acquisition duration, it appears at this time to be a useful empirical method which helps to resolve the difficult problem of EDS analysis under humid conditions. References Bower NW, Stulik DC, Doehne E: A critical evaluation of the environmental scanning electron microscope for the analysis of paint fragments in art conservation. Fresenius J Anal Chem 348, 402�410 (1994) Danilatos GD: Foundations of environmental scanning electron microscopy. Adv Electronics Electron Phys 71, 109�250 (1988) Doehne E, Bower N: Empirical evaluation of the electron skirt in the environmental SEM: Implications for energy dispersive x-ray analysis. Microbeam Anal 2, S35�36 (1993) Griffin BJ, Trautman Rl, Coffey J: X-ray resolution at low chamber pressures and chamber gas fluorescence in the ElectroScan ESEM. Microbeam Anal 2, S37�38 (1993) Messier P, Vitale T: Cracking in albumen photographs: An ESEM investigation. Microsc Res Techn 25, 374�383 (1993) Proceedings of SCANNING 96, 165 FIG. 1 The skirt correction method is tested here by placing the primary beam on a copper standard, just adjacent to aluminum metal. Thus the primary beam falls on the Cu and about 40% of the skirt falls on the Al metal. The first three spectra on the left were taken under identical conditions, except for chamber pressures of 1, 2, and 4 Torr. Note the zero Torr spectrum would contain no Al peak. Note the difference spectra created in the upper right by subtraction. The final corrected spectrum, which shows no Al signal, is presented in the lower right. These spectra were acquired using a Link Be window detector on a model E-3 ESEM from Electroscan, Inc. using DTSA and a 4pi Spectral Engine II board.

Abstract: Standard analytical equipment found in modern laboratories can answer most questions asked about samples. New equipment designs or new approaches are sometimes needed, however, to answer very specific questions that arise. Examples of four techniques with potential applications and benefits to the field of art conservation are described. The first, infrared mapping microspectroscopy, is a method used to provide a ""picture'' of the location of components in a small sample, such as a paint cross section, based on an array of infrared spectra. Environmental scanning electron microscopy (E-SEM) has the capabilities of a SEM but is especially designed to operate at near atmospheric pressures without conductive coatings on the samples. It can also be used to image dynamic processes in real time at high resolution. Organic elemental analysis (OEA or CHNS-O) provides quantitative information on the amounts of carbon (C), hydrogen (H), nitrogen (N), sulfur (S), and oxygen (O) in a combustible material that can be used for the characterization of organic materials in a sample. Photoinduced chemiluminescence (PICL) emissions produced from solid samples at room temperature can be measured by a new instrument and used to determine evidence of sample oxidative degradation long before the deterioration is manifested in any physically measurable quantity.

Abstract: Cross-sections from medieval paintings by Cenni di Francesco and Dosso Dossi were analyzed for the inorganic components as well as the binding media using an environmental scanning electron microscope (E-SEM). The advantages of this instrument compared to a normal SEM-EDX are illustrated and a number of optimization studies are reported. It was found that using a chamber gas pressure of 1.5 kPa and a tungsten source instead of the usual LaB6 source with the 38 kPa pressure normally used for imaging would significantly improve the x-ray analyses. Quantitative analyses for most of the common medieval pigments are also presented.

Abstract: The analysis of cross-sections of paint layers using microchemical and instrumental methods is important for the authentication and provenancing of works of art. The information obtained from these studies are useful not only for understanding the materials and techniques used by artists, but also are needed for developing an appropriate protocol for the restoration or conservation of the work. The cross section of a paint layer can have a very complex chemical and physical structure. It can contain the paint support, a preparation layer, underdrawing, a series of single and multicomponent paint layers, picture glazes, varnish layers, and one or more patinas. Several of these layers may be pigmented with inorganic and/or organic materials, and elemental tests as well as magnification of the layers can be very beneficial in understanding the relationship of these various layers. The environmental scanning electron microscope provides some distinct advantages over the vacuum scanning electron microscope for the analysis of painting cross sections. These include the ability to analyze and image samples without coating them with an electrical conductor, and the ability to analyze wet or outgassing samples. The latter point is not illustrated here, but it is potentially useful for the analysis of pigments on fibers or other material that may change shape as they are desiccated. In addition, the control of the vapor pressure allows dynamic reaction studies, and potentially a finer control over the ratio of backscattered electrons to secondary electrons viewed. This will allow the user to vary which things show the greatest contrast in an electron micrograph. The disadvantages include a greater capital cost, a smaller field of view (less than 600 microns in diameter with the current configuration), and an image with less contrast overall due to the background noise from the scattered electrons. When using the E-SEM for microanalysis of particles, the vapor pressure must be varied from that used for obtaining micrographs, requiring an additional optimization step. However the presence of the gas does not significantly attenuate the electron beam or change the ratio of x-ray energies emitted so that quantitative analysis is just as accurate as it has been with previous SEMs.

Abstract:

Abstract:

Abstract:

Abstract:

Abstract:

Abstract: A mineralogical survey of adobes from several historic and archaeological earthen structures in different parts of the world was undertaken to evaluate the variability in durability and resistance to weathering. The mineral composition (including clay type and quantity) and overall particle size distribution was determined for each sample. A study of the effectiveness of two chemical consolidants (an alkoxysilane and an isocyanate) on the adobe samples was also performed. Preliminary results indicate that variation in clay mineralogy and grain size distribution play significant roles in the success or failure of chemical consolidation.

Abstract: The environmental scanning electron microscope (E-SEM) provides electron imaging at relatively high sample pressure, with imaging and analysis capabilities comparable to those of traditional high vacuum SEM. Several case studies demonstrate the advantages and research potential of this new technology as applied to conservation science: 1) dynamic study of wetting and drying of consolidated and unconsolidated adobe samples; 2) semi-dynamic study of lead corrosion as a result of exposure to formaldehyde; 3) electron imaging of outgassing samples-parchment; 4) study of uncoated, non-conductive samples-swabs from Sistine Chapel cleaning; 5) X-ray analysis of uncoated insulators-gold and garnet jewelry. The environmental scanning electron microscope offers unique capabilities for dynamic experiments, imaging of outgassing samples and insulators, which may be applied to the study of deterioration mechanisms, material treatments, and ancient materials and technologies.

Abstract:

Abstract: Carbon and oxygen isotope analysis of 240m of Upper Cretaceous and Lower Tertiary limestones and marlstones from Zumaya, Spain, has revealed 3 distinct, negative carbon isotope excursions of up to 2 per mil, occurring both before and during the Cretaceous/Tertiary (K/T) transition. Ammonite and inoceramid macrofossils disappear in this section 12.5 and 120m below the K/T boundary, coincident with 2 distinct episodes of negative delta 13C values. These may reflect localized paleoceanographic or ecological changes. The last and largest of the isotope excursions corresponds with the K/T boundary marl and mass extinctions of calcareous plankton. The K/T boundary carbon isotope excursion is one of 3 that took place during the last 1Ma of the Cretaceous, each one possible being associated with biotic changes in the oceanic realm. The K/T boundary excursion coincides with iridum concentraion and spherules of unidentified origin, perhaps indicating that paleoceanographic change coincided with either extra-terrestrial impacts or volcanic events that amplified their effects and accelerated biotic changes during times of stressed oceanic ecosystems.-from Authors

Abstract: Oxygen and carbon isotope analysis of Upper Maastrichtian and lowermost Danian pelagic limestones and marls from Zumaya, Spain indicates that several major isotopic excursions occurred both before and during the Cretaceous/Tertiary (K/T) boundary event. The isotopic excursion that occurs at the Cretaceous/Tertiary boundary has previously been interpreted by most workers in terms of biologic and oceanographic changes associated with an extraterrestrial impact. Data indicate that this excursion is not significantly different from several others that preceed it, suggesting that the boundary excursion is not a unique event. These excursions are interpreted as indicators of episodic warming events of several 100 000 years duration with associated decreases in upwelling and primary productivity. Their occurrence in the latest Cretaceous may reflect the transition from the equator-dominated ocean circulation of the Cretaceous to the polar water-dominated circulation of the Cenozoic. Inoceramid and ammonite macrofossil disappearances apparently coincide with two distinct negative isotopic excursions. This suggests that their extinction in this basin was associated with surface-water warming events and decreases in productivity before the K/T boundary event. -from Authors

Abstract: Why is sodium sulfate so damaging to porous building materials? This question has remained unanswered for at least 170 years, since sodium sulfate began to be used to test the relative durability of different stones (de Thury 1828; Luquer 1895). Two important areas of recent research on this topic are 1) the non-equilibrium crystallization of thenardite (Na2SO4) and 2) the generation of high supersaturation ratios and rapid mirabilite (Na2SO4�10H2O) crystallization by placing a saturated solution of sodium sulfate in contact with fine-grained thenardite crystals. Two sets of experiments were performed to test the role of these processes: 1) macro experiments of "rising damp" crystallization of sodium sulfate in limestone blocks under conditions of high and low air exchange rate. In an attempt to determine the phase causing the important initial damage, spall fragments resulting from the high air exchange rate samples were studied by ESEM for crystal type, morphology and distribution of salt adjacent to conchoidal fractures in the calcite substrate. 2) Dynamic ESEM crystallization experiments with sodium sulfate solutions undertaken to examine the hypothesis that dissolution of thenardite in a sodium sulfate solution should be followed by rapid mirabilite precipitation. Some authors have suggested that the decay of stone from sodium sulfate occurs primarily through the crystallization of mirabilite from a supersaturated solution. Based on our "rising damp" experiments of contour scaling dynamics, this does not appear to be the case where high air exchange leads to a concentration of damage just below the surface. Instead, the non-equilibrium crystallization of small thenardite crystals appears to be responsible for the damage. Dynamic ESEM experiments with sodium sulfate confirm the rapid precipitation of euhedral mirabilite after dissolution of fine-grained thenardite in a sodium sulfate solution. This suggests that the damage caused in the standardized laboratory salt crystallization test is due to a different damage mechanism than is typically observed in decay of stone in the field.

Abstract:

Abstract:

Abstract:

Abstract: The past decade has seen a growing scientific interest in the still poorly understood subject of salt weathering, a phenomenon with significant cultural and economic consequences. This interest has led to an increase in research results and growing clarification of the roles salts play in weathering and decay. The development of improved mitigation methods to reduce the decay of building materials by salts has been a slow process, often arising from the analysis of unique field situations and otherwise dependent on simplified laboratory experiments and computer modelling. Collecting, reviewing, synthesizing and disseminating the existing data on salt weathering is a difficult task. The size and scope of the topic are mirrored in the diverse disciplines that have historically contributed to understanding the action of salts in porous materials and mitigation methods. Nevertheless, an appreciation of existing, even contradictory, data is an important tool for increasing understanding. There are now over 1800 research articles on the topic of salt weathering originating from several disciplines, as well as over 6000 references on the general problems of building material decay. In order to navigate such a vast collection of data and knowledge, this article describes the multidisciplinary nature of the study of salt damage to porous building materials, provides a framework for considering the complexity of salt damage, and serves as a selective literature survey largely focused on recent work and those articles with relevance for conservation.

Abstract: The author reviews the use of the environmental SEM microscope (ESEM) as a general research and exptl. tool in the study and conservation of cultural property. Topics include: (1) applications (sodium sulfate dynamics, formaldehyde corrosion, cleaning the Sistine Chapel, Dead Sea Scrolls), (2) ESEM and SEM: operational differences, (3) ESEM/EDS (EDS = energy dispersive spectroscopy) development (1990-1997) (dynamic imaging system, still image system, EDS spectroscopy anal.). Many refs.

Abstract:

Abstract:

Abstract:

Abstract: Energy dispersive x-ray analysis, petrographic observations, x-ray diffraction, and electron microprobe analysis were the techniques used to examine samples of tesserae from the Paphos mosaics to determine their composition, structure, and the presence of deterioration products such as soluble salts and weathering crusts. Color changes in different parts of treated and untreated mosaics received particular attention. Results are presented for the stone tesserae and for selected mortar samples. Intro: Tesserae from the Paphos mosaics, as well as a few samples from the Early Christian Basilica of Chrysopolitissa in Lower Paphos (see map, Fig. 1), were analyzed for composition, structure, and the presence of deterioration products such as soluble salts and weathering crusts. Of particular concern were color changes in different parts of treated and untreated mosaics. Stained tesserae were present in mosaics from the Houses of Theseus, Orpheus, and Dionysus. White salts were also found in the Dionysus mosaic, and yellowing was observed in the Orpheus tesserae. Such changes may be due to weathering, previous treatment, salt crystallization, or mineral staining. X-ray diffraction and electron microprobe data on the tesserae are presented here, along with suggested mechanisms for the observed color changes. Additional information on the deterioration of the Cyprus mosaics is found elsewhere in this volume (see pp. 59-60) and in other published articles (Papageorghiou 1985).

Abstract:

Abstract: Ceramics were the �high technology� material of Ancient Greece, used to produce popular drinking vessels and exotic works of art. This work seeks to characterize these understudied materials using methods such as FIB/STEM, which show promise for the nanoscale sampling and investigation of works of art. Preliminary chemical analyses of samples from Attic Greek vases often showed similar chemical composition for the red gloss and the black gloss, which are fired illite clay slips about 20 microns thick. Further analysis using the electron microprobe showed significant differences calcium and magnesium concentration between some red and black layers. FIB/STEM was used to evaluate the porosity and nanoscale structure of the two layers using representative samples of black and red gloss. The results show that the black layer is a dense glass containing 20-250 nm scale grains of magnetite-maghemite, hercynite and illmenite while the red is a more oxidized, sintered material, with ~20% porosity, containing remnant clay structures and hematite grains. The higher calcium and magnesium concentration in some red gloss layers appears to increase the melting temperature of the material, resulting in an open, sintered texture. Interestingly, the red gloss method was only used for about 200 year period starting in Athens in about 530 BC, perhaps due to its more vulnerable nature, being less firmly bonded to the ceramic substrate.

Abstract: The rapid deterioration of magnesian limestone buildings in the north of England has been a serious problem for more than one hundred years. While air quality in England has improved during this period, the rate of stone loss in these carved stone structures has not slowed. Thus far, conventional stone conservation treatments have not been successful in mitigating this decay, and large-scale stone replacement has been proposed to deal with the problem for buildings such as York Minster and the world heritage site of Fountains Abbey. The use of a solar-powered, field time-lapse camera correlated with separately acquired environmental monitoring data, allowed the analysis of the pattern and rate of loss of stone from the surface of Howden Minster, an abandoned monastery in Yorkshire dating to 1380 AD. Acquiring a photograph every 1-3 hours over the course of a year allowed the stone damage to be correlated with local environmental conditions. Preliminary results indicate that loss is episodic rather than continuous and in some cases is related to unusual environmental conditions, such as high winds and condensation events. Damage was found also to be synchronous, with surface change (flaking, granular disintegration, and loss of flakes) occurring at the same time in different stone blocks. Crystallization pressures from magnesium sulfate phase transitions appear to be the main cause of the loss of stone surfaces. It should be noted that quantitative data on rates of surface loss are not available from most monuments. Time-lapse methods permit the relatively inexpensive acquisition of this type of data, which is needed to aid conservation decision-making and the evaluation of interventions. Such tools should also prove useful to geomorphologists studying honeycomb weathering, the moving rocks on Death Valley's Racetrack Playa, and other phenomena that are otherwise difficult to study.

Abstract:

Abstract: The Chapter House at Howden Minster is a small octagonal 14th century magnesian limestone building. The architectural decoration on the interior walls is among the finest of its period in England. The building has been a ruin since the 18th century, and its elaborate interior stone carving has suffered from ongoing erosion. The deterioration of the stonework is severe and an evaluation of historic photographs reveals the flaking has recently accelerated. To understand the reasons why the stone degradation is so serious, we are examining the decay mechanisms of the stone in the laboratory, subjecting magnesian limestone blocks to environmental changes that typically drive stresses on the stone, i.e. evaporation, moisture transport, and salt crystallisation. On site we are using a microclimatic survey in conjunction with detailed condition recording, to try to establish the specific microclimatic factors and events that trigger the damage.

Abstract: Constructed entirely of magnesian limestone, the Chapter House at Howden Minster, East Yorkshire, dates from 1380 and has been in the care of English Heritage since 1971. For two hundred and fifty years, it was a roofless ruin; the elaborately carved stone interior subject to significant on-going decay. The acute stone degradation on this site prompted English Heritage and the Getty Conservation Institute to establish a joint project in 2003 to understand the mechanism of magnesian limestone decay. The aim of this project is to understand the causes and mechanism of the deterioration at Howden Minster and devise a conservation strategy for the site that would help our general understanding of how to conserve deteriorating dolomitic limestone structures. Results from decay mechanism studies in the laboratory show that flaking of Magnesian Limestone can be achieved in three months using magnesium sulfate salts and fluctuating moisture levels. Petrographic investigations have included characterisation of the properties of magnesian limestone samples from Howden compared to freshly cut stone from local quarries and stone from other historic sites. On site, the patterns and rate of decay have been mapped and documented. The condition of the stone is recorded and compared to the existing historic photographic record. Methods of recording active decay are being compared, including condition survey, photogrammetry, laser scanning, repeat photography, and field-time lapse photography. Changing environmental conditions are monitored, including relative humidity, ambient temperature, radiant temperature, and surface temperature. A weather station also measures external temperature, humidity, rainfall, wind speed and direction at the site. Atmospheric pollutant levels are also recorded. Changing moisture levels and placement of moisture, at heights and at depth within the wall, are monitored. The type, concentration, and location of salts have been examined before and after large-scale desalination trials. There are a number of issues driving the stone decay, including concentration and mobility of magnesium sulphate, activity of salts instigated by humidity fluctuations, periodic condensation on the stone, historic pollution levels and site-specific physical factors.

Abstract: Within the framework of the EU project �Desalination�, Madame John�s Legacy, a historic brick and timber home in the French Quarter of New Orleans was selected as a field site to evaluate the effectiveness of four desalination poultices under warm and humid environmental conditions. The poultices were applied to salt-laden brick walls in a sheltered exterior environment and in an air-conditioned ground floor. Effectiveness was defined by the percentage of salts removed as well as the depth of desalination. Preliminary results from the investigation presented here demonstrate the importance of environmental conditions, shrinkage, adhesion and drying rates in poultice effectiveness. Desalinating masonry in a humid environment led to leaving the poultice on to dry for months instead of weeks, resulting in a significant reduction in salt content of well over 90% for two poultices.

Abstract: Time-lapse imaging has been used to provide a record of damage to stone as it is occurring in the field. This type of imaging serves to document changes in the condition of the stone, and provides a means for understanding why the changes are occurring--invaluable evidence for devising interventions to deter damage, and to assess the success of conservation interventions. At the site of Howden Minster, UK, this technique is being used to evaluate the pattern and rate of stone loss, where the flaking of Magnesian Limestone is both rapid and severe. The damage to the stone is recorded on site with timed macro-imaging and can be correlated stone with local environmental conditions recorded on a environmental monitoring system. Preliminary results indicate that loss is episodic rather than continuous and synchronous, with surface change occurring at the same time in different stone blocks. This damage can be related to harsh variable environmental conditions, such as high winds.

Abstract: The behavior and development of thenardite (anhydrous sodium sulfate) from mirabilite (sodium sulfate decahydrate) under the Environmental Scanning Electron Microscope (ESEM) during humidity cycling (50-100%) was observed. After 7 cycles a microcrystalline porous structure of thenardite was formed with an increased surface area and volume compared to mirabilite. At this point expansion and contraction take place with raising and lowering the relative humidity (RH). Hydration and dehydration reactions of sodium sulfate were determined by weight changes, after storage of this salt in RE control chambers. The critical RH value of 75% was found to be the inflection point for the expansion/contraction and hydration/dehydration reactions (observed under the ESEM and in the RH chambers, respectively). The rates of these reactions become more rapid above and below 75% RH as the humidity was increased or decreased. After 20 cycles expansion and contraction and the associated change in volume no longer ocurred. On continuing RH cycling the microcrystalline structure moved suggesting attraction and repulsion between similar structures with the increase and decrease of RH, respectively. The rapid physical movements observed under the ESEM suggest that they may play an important role in the damage process due to humidity changes.

Abstract:

Abstract: The Hieroglyphic Stairway at Copan in Northwest Honduras is the longest inscription known from the Ancient Maya. As part of a larger conservation project of the Institute Hondureiio de Antropologia e Historia (IHAH) and the Getty Conservation Institute (GCI), blocks of uncarved green and buff volcanic tuff as well as samples of flaking tuff from the Hieroglyphic Stairway, were characterized for their material properties and state of decay. Flaking appears to be connected to selective dissolution, hygric cycling, lichen hyphae and calcite precipitation in stone fractures. These results represent the first comprehensive characterization of these materials and aid the understanding of material durability, behavior and conservation for this important site.

Abstract: Why is sodium sulfate so damaging to porous building materials? This question has remained unanswered for at least 170 years, since sodium sulfate began to be used to test the relative durability of different stones (de Thury 1828; Luquer 1895). Two important areas of recent research on this topic are 1) the non-equilibrium crystallization of thenardite (Na2SO4) and 2) the generation of high supersaturation ratios and rapid mirabilite (Na2SO4�10H2O) crystallization by placing a saturated solution of sodium sulfate in contact with fine-grained thenardite crystals. Two sets of experiments were performed to test the role of these processes: 1) macro experiments of "rising damp" crystallization of sodium sulfate in limestone blocks under conditions of high and low air exchange rate. In an attempt to determine the phase causing the important initial damage, spall fragments resulting from the high air exchange rate samples were studied by ESEM for crystal type, morphology and distribution of salt adjacent to conchoidal fractures in the calcite substrate. 2) Dynamic ESEM crystallization experiments with sodium sulfate solutions undertaken to examine the hypothesis that dissolution of thenardite in a sodium sulfate solution should be followed by rapid mirabilite precipitation. Some authors have suggested that the decay of stone from sodium sulfate occurs primarily through the crystallization of mirabilite from a supersaturated solution. Based on our "rising damp" experiments of contour scaling dynamics, this does not appear to be the case where high air exchange leads to a concentration of damage just below the surface. Instead, the non-equilibrium crystallization of small thenardite crystals appears to be responsible for the damage. Dynamic ESEM experiments with sodium sulfate confirm the rapid precipitation of euhedral mirabilite after dissolution of fine-grained thenardite in a sodium sulfate solution. This suggests that the damage caused in the standardized laboratory salt crystallization test is due to a different damage mechanism than is typically observed in decay of stone in the field.

Abstract:

Abstract: Introduction: "In time, and with water, everything changes." ---Leonardo da Vinci. The crystallization of soluble salts in porous building materials is a widespread weathering process that re- sults in damage to important monuments and archaeo- logical sites [1]. Salt weathering by thenardite (sodium sulfate) and mirabilite (sodium sulfate decahydrate) is especially destructive, yet is still not fully understood [2]. Halite (sodium chloride) in contrast, is one of the least damaging salts [3]. Previous work has also dem- onstrated the importance of airflow in salt weathering [4]. Here we present new data that help explain why sodium sulfate is so damaging and also show how crystallization modifiers and changes in airflow can reduce salt damage in laboratory experiments. Damage Mechanism: The behavior of sodium sul- fate was documented using saturated solutions and oolites from Monks Park limestone (a stone well known to be vulnerable to salt damage) as test sam- ples. Damage was evaluated based on the degree of cracking of the oolite. Observations of sodium sulfate behavior using the environmental scanning electron microscope (ESEM) and time-lapse video methods show that damage during wet/dry cycling generally only occurs after larger mirabilite crystals (~10 mi- crons) undergo dehydration to thenardite, producing a high-surface area substrate of sub-micron crystals with strong capillary suction. When wetted, these thenardite crystals generally dissolve, rather than hydrate, result- ing in extremely rapid crystallization, as observed in the ESEM. Simple crystallization and dissolution of mirabilite, without dehydration appears to cause little damage after 10 cycles. Salt damage theory suggests that the limiting fac- tor in causing damage is the need to sustain a solution in situ with a high supersaturation ratio [3]. This is generally difficult in many porous materials since their naturally rough surfaces tend to enhance crystallization once saturation is reached. Rapid cooling is one way to accomplish high supersaturation ratio in the sodium sulfate system. However, our in situ observations sug- gest that the process of cyclic dehydration followed by contact with a saturated solution of sodium sulfate can result in substantial damage to porous materials. Miti- gation methods such as limiting the rapid cooling or rapid drying of porous, salt-laden stone through the use of shelters may reduce the damage potential of sodium sulfate. Reducing Damage: Crystallization modifiers can significantly effect the capillary passage of dilute and concentrated solutions of sodium chloride and sodium sulfate through columns of limestone. The limestones were oolitic Monks Park stone where 90% of its pores measured between 0.05-0.80 microns and Texas Creme, a fossilferous stone with 90% of its pore size distribution measuring between 0.5 and 3.0 microns. In the absence of modifiers, sodium chloride passage through Monks Park limestone gave predominantly subflorescence with mild edge erosion while sodium sulfate mainly effloresced and severely damaged the stone column. With Texas Creme limestone, essen- tially only efflorescence occurred with either salt and there was little or no stone damage. Most crystallization inhibitors--used in industry to prevent scaling by promoting high supersaturation levels for calcium compounds--plugged the columns or were otherwise without effect on the passage of salt solutions. Only alkali ferrocyanides were found to im- pact significantly on the interaction of these solutions as they moved through the limestone. The addition of 0.01-1.00% of K4Fe(CN)6 to sodium chloride in Monks Park limestone experiments increased the flow rate of solutions through the stone, resulting in slightly yellow-colored efflorescence in place of subflo- rescence, and yielded a massive formation of extended dendritic filaments without damaging the stone. This protection by additive was extended to sodium sulfate solutions, but only at lower salt concentrations. Re- sults comparable to the effect of adding K4Fe(CN)6 to concentrated sodium chloride Monks Park limestone experiments were obtained with saturated sodium sul- fate solutions without additives by conducting the experiments in a draft-free, high humidity environ- ment--suggesting a potentially useful strategy for the conservation of fragile, salt-laden objects. These results are explained by factors causing evaporation of solu- tion to occur either below or at the surface of the stone, and by the effect of modifiers on the crystal habit of the salts forming during evaporation in this region. References: [1] Doehne E. (1994) In situ dynamics of sodium sul- fate hydration and dehydration in stone pores: Observa- tions at high magnification using the environmental scanning electron microscope, in Fassina V., ed., The Conservation of Monuments in the Mediterranean Basin, 143-150. [2] Rodriguez-Navarro C., Doehne E., and Sebastian E. (2000) Cement and Concrete Re- search 30, 1527-1534. [3] Rodriguez-Navarro C. and Doehne E. (1999) Earth Surf. Processes Landforms 24, 191-209. [4] Rodriguez-Navarro C., Doehne E., and Sebastian E. (1999) Bulletin of the Geological Society of America 111, 1250-1255.

Abstract: ESEM analysis and damage simulation with stone samples from the Mayan city of Copan, Honduras Eric Doehne, David Carson, Getty Conservation Institute, Los Angeles, CA The carved stone glyphs that make up the Hieroglyphic Stairway at the archaeological site of Copan in western Honduras form the longest Maya text in existence. Unfortunately, the surfaces of many of the glyphs{which date from 746-756 AD{appear to be eroding rapidly due to deterioration phenomena that are not well understood. A collaborative project to analyze the problem was developed in coordination with the Honduran authorities and preliminary documentation and characterization studies using a range of methods are underway. Results using ESEM/EDS analysis show the main stone at Copan is a green, relatively homogeneous rhyolitic to andesitic welded tuff containing a matrix composed of heulandite, quartz and plagioclase with quartz xenocrysts and phenocrysts of biotite and clinopyroxenes, as well as plagioclase and potassium feldspars. Fine crystals of ilmanite are also common. Comparison of microsamples of weathered stone to fresh stone show some differences that help explain the loss of material from the glyphs. Biotite crystals are often altered to chlorite and iron hydroxides (goethite) often with a change in crystal volume. The presence of gypsum at the top of the stairs suggests salt damage as an important mechanism related to the presence of concrete. This damage mechanism has been simulated through dynamic ESEM experiments. The identification of a vein-filling calcium compound (apparently calcite with intermixed calcium oxalate and calcium phosphate) associated with aking elsewhere on the stairway may be related to damage from sub-surface microbial communities and organic material. Additional ESEM studies are in progress to determine the relative importance of these deterioration mechanisms.

Abstract: Las causas y factores que influyen en el transporte, evaporación, y posterior cristalización de soluciones salinas en un medio poroso, han sido analizadas observando la precipitación y crecimiento de halita y mirabilita, sobre lamina delgada, en capilares de vidrio y en un soporte pétreo (Bath stone, caliza oolitica). El análisis de la morfología de los cristales, su emplazamiento y los daños que cada una de las sales provocan al crecer en un medio poroso, permiten diferenciar claramente los efectos y mecanismos de alteración debidos a cada una de ellas. Gran cantidad de cristales de Na2SO4.H20 precipitan simultaneamente y de forma sistematica como subeflorescencias, provocando enormes daños, Sin embargo, los cristales de NaCl se distribuyen homogeneamente por el sistema poroso de la roca, o bien forman eflorescencias, sin generar daños. Estos resultados son discutidos en base a las teorías mas actuales sobre alteración por crecimiento de sales.

Abstract:

Abstract: The limestone used in the construction of much of the 8-11th century Maya structures at Xunantunich, Belize is mechanically weak. Active microfloral growth, cyclic changes in humidity and temperature, and exposure to the erosive effects of wind and rain have resulted in deterioration of the stone used at the site. Limestone samples were consolidated using water-compatible and other consolidants and were exposed to both sunny and shaded tropical environments for one year. Data-logging meteorological stations were used to monitor the temperature, relative humidity, rainfall, wind conditions and solar irradiance during the exposures. Accelerated aging tests on similarly treated specimens were performed in the laboratory. Dilute epoxy and acrylic resin systems in hydrophilic solvents were found to penetrate and consolidate weak limestone. Several biocides applied in dilute aqueous solution were effective in preventing microfloral growth on new limestone and for controlling in situ growth on historic limestone.

Abstract: The Environmental Scanning Electron Microscope (E-SEM) is a significant advance in electron microscopy and its operation is based on three phenomena: 1) when traveling through a gas of moderate density (typically 100-1600 Pa H2O), an electron beam will develop a broad skirt of scattered electrons while the central beam retains its original diameter; 2) when secondary electrons are emitted from the sample and travel through this moderately dense gas, they will ionize a fraction of the gas molecules, thus creating additional 'environmental' secondary electrons and positive ions. The positive ions are attracted to the negatively charged surface of the sample and form a thin, conductive film that neutralizes the surface charge. The 'environmental' secondary electrons may collide with other gas molecules, which leads to a cascade effect and amplification of the secondary electron signal; 3) the original secondary electrons and the 'environmental' secondary electrons can be detected by a small, positively biased metal disk which sits above the sample and is insensitive to light. Noise created by backscattered and skirt electrons can be detected separately and electronically subtracted to improve the signal-to-noise ratio.

Abstract: Observations of sodium sulfate hydration, dehydration, dissolution and crystallization at magnifications of 200-10,000x have revealed previously undescribed material behaviors that help explain the destructive effects of this salt in wall paintings, historic structures and monuments. Experiments performed in the environmental scanning electron microscope show that large crystals of anhydrous sodium sulfate, when exposed to water vapor, initially form a skin of sodium sulfate decahydrate that prevents the complete hydration of the crystal until sufficient liquid water is present to dissolve the skin. Hydration of sodium sulfate is also initially much slower than dehydration during similar rates of humidity change. Sodium sulfate decahydrate consistently breaks down during dehydration to form sub-micron aggregates of anhydrous sodium sulfate. Provided that the decahydrate form is not dissolved by excess liquid water, subsequent hydration-dehydration cycles result in a highly porous, high-surface area salt structure consisting of sub-micron particles. Once this porous sodium sulfate structure is established, hydration and dehydration occur at roughly the same rate. Dissolution of the fine-grained structure by liquid water, followed by drying, results in the rapid crystallization of much larger (10-100µm) sodium sulfate decahydrate crystals with well-defined crystal faces.

Abstract: Observations of sodium sulfate hydration, dehydration, dissolution and crystallization at magnifications of 200-10,000x have revealed previously undescribed material behaviors that help explain the destructive effects of this salt in wall paintings, historic structures and monuments. Experiments performed in the environmental scanning electron microscope show that large crystals of anhydrous sodium sulfate, when exposed to water vapor, initially form a skin of sodium sulfate decahydrate that prevents the complete hydration of the crystal until sufficient liquid water is present to dissolve the skin. Hydration of sodium sulfate is also initially much slower than dehydration during similar rates of humidity change. Sodium sulfate decahydrate consistently breaks down during dehydration to form sub-micron aggregates of anhydrous sodium sulfate. Provided that the decahydrate form is not dissolved by excess liquid water, subsequent hydration-dehydration cycles result in a highly porous, high-surface area salt structure consisting of sub-micron particles. Once this porous sodium sulfate structure is established, hydration and dehydration occur at roughly the same rate. Dissolution of the fine-grained structure by liquid water, followed by drying, results in the rapid crystallization of much larger (10-100µm) sodium sulfate decahydrate crystals with well-defined crystal faces.

Abstract:

Abstract: Dynamic studies permit the observation of microscopical changes of materials over time as various factors alter an object. Using this methodology, processes important in art conservation and archaeology such as the wetting and drying of consolidated and unconsolidated building materials or the corrosion of metals from air pollutants can be studied in situ and in tempora. the development of the environmental scanning electron microscope (E-SEM) has made it possible to videotape these dynamic processes at nearly the same resolution limits as traditional SEM technologies without elaborate sample preparation. Experiments examining salt crystallization, shrinkage in adobe, and lead corrosion illustrate the value and applicability of the new E-SEM technology.

Abstract:

Abstract:

Abstract:

Abstract:

Abstract:

Abstract:

Abstract:

Abstract:

Abstract: THE TORUN GUIDELINES FOR CONFERENCES IN THE FIELD OF STONE CONSERVATION With the aim of improving the quality and the dissemination of knowledge through congresses in the field of stone conservation, the 11th International Congress on Deterioration and Conservation of Stone, and the 13th meeting of the ICOMOS International Stone Committee, which met in Torun on September 15th to 20th 2008, adopted the following text. INTRODUCTION In an era of increasing information and changing dissemination technology it seems an appropriate moment to reflect on ways to improve the quality and accessibility of knowledge in the field of stone conservation. As knowledge increases rapidly, teams working on stone conservation have become more specialised and often present their results at specialist meetings. This trend may increase the potential for isolated perspectives and the risk that knowledge may not reach its intended goals. The general congresses on stone deterioration and conservation, organised every 4 years since 1972 give a useful snapshot of the different trends of stone conservation and provide a multidisciplinary forum for discussion, complementing the specialist meetings. However, it can be difficult for them to encompass all the different trends and fields of stone conservation. In recent decades there have been a number of calls to improve the quality and impact of knowledge in the conservation field. In response, there have been a number of improvements, such as more review articles and multi-author textbooks which give new researchers some of the background needed. Electronic publication of full text articles from most journals makes the peer-reviewed literature more readily available. Nevertheless, most conference proceedings still have limited electronic distribution. THE GUIDELINES 1 Planning When planning conferences organisers should review other conferences already scheduled in the field, in order to separate their own conference from others by at least six months. The aim is to increase the potential pool of participants and to increase the likelihood of original research being presented. 2 Selection of papers The selection of papers for formal conferences should be based on a thorough review by at least two experts. Organisers, assisted by their scientific committees, should check for and refuse �doublons�, i.e. papers that have been, or are about to be, published in proceedings of another conference. Published papers (whether oral or poster) should meet minimum standards, including: � precisely defined research methodologies � appropriate reference citations � advancing knowledge in the field. 3 Communication among participants Organisers should encourage formal and informal communication among conference participants. These may include discussion sessions, panel discussions and workshops. 4 Seeking quality and measuring outcomes Organisers, assisted by their scientific committees, should ensure good quality papers. In addition, organisers should measure the outcomes of their conference. Measures adopted may include reviews of the conference and opportunities for user feedback, such as a web page for participant responses, and quality rankings. 5 Dissemination strategy To facilitate rapid dissemination of the ideas presented at the conference, organisers should plan for electronic dissemination of the proceedings. This should be arranged within a short period of time (e.g. a year) to ensure that the results achieve a wide and long-lasting distribution. The following persons participated to the drafting of the Torun Guidelines : Akos Török, Hungary - Clifford Price, UK - Dagmar Michoïnova, Czech republic - Daniel Kwiatkowski, Sweden - David Young, Australia - Elsa Bourguignon, France - Eric Doehne, USA - Hilde De Clercq, Belgium - Jadwiga W. Lukaszewicz, Poland - Jean-Marc Vallet, France - Jo-Ann Cassar, Malta - Johannes Weber, Austria - Jose Delgado- Rodrigues, Portugal - Milos Drdacky, Czech republic - Marisa Laurenzi-Tabasso, Italy - Myrsini Varti-Matarangas, Greece - Philippe Bromblet, France - Stefan Simon, Germany - Vasco Fassina, Italy - Vasu Poshyanandana, Thaïland - Véronique Vergès-Belmin, France.

Abstract: