4.10 New Methods of Organic and Inorganic Microanalysis
The Getty Conservation Institute
Period of Activity: Current Research
To develop a methodology for binding media analysis, a detailed literature search will be conducted to find: (a) all methods that have been used in the conservation field for binding media analysis, (b) methods that have been used successfully in industrial and research laboratories and can be modified for conservation applications, and (c) emerging instrumental methods that have the potential to replace or complement current methodologies. A short list of approaches includes:
a. staining microscopic methods
b. paper and thin-layer chromatography (TLC)
c. gas chromatography (GC)
d. high performance liquid chromatography (HPLC)
e. electrophoresis electrophoresis;
f. Fourier transform infrared spectrometry and FTIR microanalysis
g. mass spectrometry (FAB-MS, Solid Probe MS, GC-MS, and LC-MS)
h. differential thermal analysis (DTA) ;
i. thermal mechanical analysis (TMA)
Derrick, M. R., C. M. Druzik, and F. Preusser, "FTIR Analysis of Authentic and Simulated Black Lacquer Finishes on Eighteenth Century Furniture," Urushi, Proceedings of the Urushi Study Group, Tokyo, The Getty Conservation Institute, June 10-27, 1985, pp. 227-234.
ABSTRACT-Compositional analysis on the finishes of Oriental style furniture (made in Europe circa 1750) from the J. Paul Getty Museum, was done by Fourier transform infrared (FTIR) spectrophotometry. Two microanalytical techniques, in conjunction with the high resolution and great sensitivity of FTIR, were applied to minimal sample quantities. These two techniques for sample preparation, KBr micropellets and a diamond cell, gave comparable IR spectral results. The finishes on these objects were found to fall into three general categories: (1) Urushi-based resinfinish on the entire piece, (2) Urushi-based resin finish on inset panels only, and (3) non-Urushi finishes.
Derrick, M. R., "Spectroscopy in Archaeometry and Art Conservation," Society of Applied Spectroscopy, Lake Arrowhead, California, May 23, 1987.
Derrick, M. R., "Infrared Spectral Analysis of Natural Resins Used in Furniture Finishes," Wood Artifacts Group, Paper presented to American Institute for Conservation 16th Annual Meeting, New Orleans, Louisiana, June 1-5, 1988.
ABSTRACT-Identification of components in furniture finishes can be a tedious and arduous task since these coatings were often prepared from secret recipes containing several ingredients which may have changed or degraded with time. This study thoroughly examines the capabilities and limitations of infrared spectroscopy for the identification of natural resins used in these mixtures. A Fourier transform infrared spectrophotometer, with its inherent high resolution, excellent energy throughput, accurate band reproducibility, and computer enhancements, was used to establish a specific list of absorbance band positions for the identification of resins, waxes, oils, and gums. This list of band positions was then applied to the analysis of pure samples of the most common resins in eighteenth-century furniture finishes (shellac, sandarac, copal, mastic, and rosin ) to determine the spectral reproducibility, analysis error, and detection limits (minimal sample size) for the instrument. With this basic information, mixtures of two, three, and four components were prepared and analyzed to determine the limits of quantification for each resin. Computer methods such as spectral subtraction and deconvolution were used to augment this process. Next, the possible factors introduced into the spectra by varnish preparation (solvent extraction and filtration) and aging of the coating (oxidation and deterioration) were examined. This information was then compiled to provide a viable FTIR identification method for these resins in furniture finishes.
Derrick, M. R., "Fourier Transform Infrared Spectral Analysis of Natural Resins Used in Furniture Finishes," Journal of the American Institute for Conservation, Vol. 28, 1989, pp. 43-56.
ABSTRACT-Infrared spectroscopy is a valuable method for the selection and identification of organic coating materials. The vibrational bands that appear in the infrared spectra provide information on chemical functional groups of a sample which may allow for general characterization of the material or even the identification of specific compounds. Mixtures of natural materials, as are often found in furniture finishes, can stretch conventional infrared spectroscopy to its limits as an analytical method. This paper outlines the capabilities and limitations of Fourier transform infrared spectroscopy for the identification of natural resins used in historic furniture finishes.
Schilling, M. R., "The Glass Transition of Materials Used in Conservation," Studies in Conservation, Vol. 34, 1989, pp. 110-116.
ABSTRACT-The glass transition temperature, Tg, has a profound effect on many physical properties of polymeric conservation materials. Presently, it is difficult to find a reliable source of Tg data because a standard procedure for evaluating the raw analytical data is lacking. To further complicate matters, comparison of Tg data taken from different sources is nearly impossible because the results can vary between analytical methods. In this study, a variety of conservation materials were used and analyzed by differential scanning calorimetry (DSC), and the Tg data were evaluated using the standard method established by the International Confederation for Thermal Analysis (ICTA). The complete set of data can be used to aid conservators in selecting materials for a particular application.
Schilling, M. R., "Effects of Sample Size and Packing in the Thermogravimetric Analysis of Calcium Montmorillonite STx-1," Technical note in Clays and Clay Minerals, Vol. 38, Nº 5, 1990, pp. 556-558.
ABSTRACT-In thermogravimetric analysis (TGA) of Ca-montmorillonite (STx-1) from the Source Clays Repository of the Clay Minerals Society, discrepancies have been observed between data collected at the Getty Conservation Institute and corresponding curves found in the clay data handbook of Mackenzie and Caillere (1979). Specifically, the three weight-loss steps associated with loss of water are as much as 115 °C higher in the clay handbook. The differences in temperature were attributed to the effects of sample size and packing. Although it is well known in the field of thermal analysis that sample size and preparation can have a pronounced effect on thermoanalytic data, it may be less obvious to those outside the field. The purpose of this note is to report how these parameters affect TGA curves of clays.
Schilling, M. R., "Analysis of Polymeric and Composite Materials Using Thermogravimetry," M.S. Thesis, California State Polytechnic University, Pomona, California, 1990.
ABSTRACT-Thermogravimetric Analysis of Calcium Montmorillonite Treated with Hexamethylene Diisocyanate: The product of the reaction between calcium montmorillonite and hexamethylene diisocyanate is acetone, catalyzed with dibutyltin dilaurate, and was studied by thermogravimetry to determine the amount of polymer produced. The method developed to determine polymer content in the clay is completely general, possesses excellent accuracy and precision, and produces more consistent results than traditional gravimetric methods.
Analysis of High-Performance Liquid Chromatography Bonded Stationary Phases Using Thermogravimetry. A thermogravimetric method was developed for the determination of C-18 bonded phase content of high performance liquid chromatography stationary phases. The method possessed excellent accuracy and precision, compared to traditional carbon and hydrogen analysis. Thermogravimetry was employed as a means of determining the optimum drying temperature for bonded stationary phases, in order to improve the accuracy of carbon and hydrogen analysis.
A Novel Thermogravimetric Technique for Qualitative Analysis of Polymeric Materials. A novel thermogravimetric technique, known as "subtractive thermogravimetry," or STG, was developed for qualitative analysis of polymers. STG curves were obtained by subtraction of the TG data for a given polymer analyzed in nitrogen from the TG data for the same polymer analyzed in oxygen. STG curves, shown to be characteristic for a given polymer, could be reduced to sets of significant event temperatures (onset and peak temperature data) which can be used to facilitate polymer identification. The method can be used with high heating rates in order to maximize sample throughput.
Derrick, M. R., and D. C. Stulik, "Identification of Natural Gums in Works of Art Using Pyrolysis-Gas Chromatography," Preprints, ICOM 9th Triennial Meeting, Working Group 1, Dresden, Vol. 1, August 26-31, 1990, pp. 9-13.
ABSTRACT-Pyrolysis-gas chromatography was used for identification of natural gum types (gum arabic, ghatti, guar, karaya, and tragacanth ). Regardless of chemical and structural similarities between different gum types, the identification of gum based on manual or computer-aided pyrogram matching of peak and intensity patterns is possible. Identification of gums is feasible from samples as small as 1 mg. Pyrolysis at lower temperatures (400 °C) provides a better match between analytical results obtained of pure gums and gum-pigment mixtures.
Khanjian, H. P., "Determination of Binding Media Concentrations in Gesso," Paper presented at the WAAC Annual Meeting, Catalina Island, California, October, 15-17, 1990.
ABSTRACT-The concentration of binding medium in gesso is potentially an important parameter for studying historical artist or workshop techniques. This paper presents a rapid method for quantifying binding medium in gessos using Fourier transform infrared spectrophotometry (FTIR). Four types of gessos (CaCO3-rabbit skin glue; CaCO3-gum arabic; CaSO4-rabbit skin glue; CaSO4-gum arabic) were prepared with concentrations of binder ranging from 0.5 to 50.0 w/w%. Binding medium content in the gesso standards was verified using thermogravimetry. The peak heights of binder and pigment in the FTIR spectra were ratioed to establish a calibration curve. The curve was used to quantify the amount of binder in museum samples.
Schilling, M. R., "Analysis of Drying Oils by Gas Chromatography-Mass Spectrometry," Paper presented at the WAAC Annual Meeting, Catalina Island, California, October 15-17, 1990.
ABSTRACT-Linseed walnut, and poppyseed oils obtained from various suppliers were classified according to their fatty acid profiles, using combined gas chromatography-mass spectrometry. The results indicated that, for a particular oil, the ratio of palmitic to stearic acid concentration (P/S) is affected by heat aging and ultraviolet light exposure. The variation in P/S ratio is also affected by the method for pretreatment of the oil. Included in this paper is a discussion of the method of sample preparation which greatly reduces the overall analysis time.
Derrick, M., "Infrared Analysis of Fragments from the Dead Sea Scrolls," Paper presented at the WAAC Annual Meeting, Catalina Island, California, October 15-17, 1990.
ABSTRACT-Infrared analysis was done on nine sample fragments from the Dead Sea scrolls. FTIR and micro FTIR were used to obtain information on the state of deterioration of the samples and to identify any materials which may have been added to the parchment during preparation. Examination of the amide I and amide II absorbance band heights and positions showed indications of collagen modifications along with hydrolysis and oxidation in the samples. Three nonproteinaceous materials-chalk, talcs, and ammonium sulfate were identified in the fragments in varying amounts. The results show that FTIR is a useful method for providing an indication of the conditions and materials found in old parchment samples.
Derrick, M. R., J. M. Landry, and D. C. Stulik, Methods in Scientific Examination of Works of Art: Infrared Microspectroscopy, Workshop and Textbook, the Getty Conservation Institute and the Loyola Marymount University, January 8-11, 1991.
Stulik, D. C., C. M. G. Druzik, M. R. Derrick, and J. M. Landry, "Standard Materials for Analysis of Binding Media and GCI Binding Media Library," Paper presented at the American Institute for Conservation Annual Conference, Albuquerque, New Mexico, June 3-8, 1991.
ABSTRACT-Identification of binding media in paint layers is a very important task before any restoration and conservation treatment, not only for detailed studies of artist techniques, but also for authentification authentification; purposes. Binding media used throughout the ages ranged from chemically complicated natural products to modern polymeric materials. This makes binding media identification very challenging and demands well-characterized standard materials. Rutherford J. Gettens started the first important collection of binding media in the late 1920s at Harvard's Fogg Art Museum Fogg Art Museum;. The collection's contents and organization are critically analyzed in this paper. Knowledge gained during our work with the Gettens Collection has been implemented in the design and initial work on a new GCI Binding Media Library which will serve our field in the future. Organization of the library, its documentation, and access, are discussed in detail. Future development of the library depends on a national and international collaboration between all institutions and individuals which are actively involved in characterization of binding media or seek binding media information for their restoration or conservation work.
Khanjian, H. P., "Examination of Oxalate Crust on Weathered Stone Weathered Stone; Surfaces," Paper presented at the WAAC Annual Conference, Seattle, Washington, September 29-October 1, 1991.
ABSTRACT - Deterioration of stone surfaces has been the focus of a number of scientific studies. One related problem is the formation of oxalate crusts on calcareous rock surfaces which is a by-product of lichen growth. This paper presents a new method for the identification of oxalate layers in cross-sections of lichen-damaged limestone using Fourier transform infrared (FTIR) micro-spectroscopy. Numerous samples of limestone containing lichen growth have been collected from statues, monuments, and quarries. Samples were mounted, polished, and cross-sectioned in preparation for analysis. A combination of computer controlled x-y stage and two-dimensional FTIR mapping has been used to analyze the cross-sections. The system allowed the identification of deteriorated layers as small as 10 mm in width. FTIR analysis was complemented by UV fluorescence studies of the oxalate deposits on weathered stones.
Wallert, A., Kookboeken en Koorboeken: Techniek en Productie van boekverluchting in koorboeken van het klooster Monte Oliveto Maggiore, Groningen University Press, Groningen, 1991.
Wallert, A., "Cimatura de Grana: Identification of Natural Organic Colorants and Binding Media in Medieval Manuscript Illumination," Zeitschrift fuer Kunsttechnologie und Konservierung, Vol. 5, 1991, pp. 74-83.
ABSTRACT-Medieval technical treatises can provide valuable information on the use of natural dyestuffs in manuscript illumination. Many Italian illuminators' treatises describe the application of organic colorants in "cimatura de grana"-colors. Based on the information from such historical descriptions, fluorescence spectrometry makes it possible to identify natural organic dyestuffs in samples from medieval manuscript illuminations. Some purplish-red colored paint samples that were under examination were shown to be made by using Polish cochineal as the colorant. It seems that kermes had been used in places where a more red color was needed. It appeared to be possible to identify by fluorescence spectrometry the presence of hexoses in these samples. This was taken as an indication for the use of gum as binding medium in the "cimatura de grana"-colors. This was in agreement with contemporary descriptions. Fluorescence measurements of binding media were taken in the same solvent that was used for the analysis of the colorants. Thus the risk of loss of sample or of sample contamination could be avoided. Measurements could be taken from the same sample identifying both colorant and binding medium. Fluorescence of dyestuffs and binding media can be described by three parameters, i.e., excitation wavelength, emission wavelength, and quantum efficiency. A complete rendering therefore requires a three-dimensional representation.
Wallert, A., "Identification of Binding Media in Mediaeval Manuscript Illuminations by Three-Dimensional Solution Fluorescence Spectrometry," submitted to Studies in Conservation, 1992.
ABSTRACT-Identification of binding media in miniatures can be accomplished by solution fluorescence spectrophotometry solution fluorescence spectrophotometry;. Problems in evaluation of media analysis are discussed. All binding media used in manuscript illumination can be made to transform with various reagents into very luminescent compounds. A description of the methods is illustrated by examples of analysis thereby showing its possibilities and limitations. Identification of binding media is based on a comparison of the fluorescent spectra with those of known binders. Three-dimensional and contour plotting allow an even more precise examination of organic substances. Spectrofluorometry provides a rapid, effective means for qualitative determination of binding media in very small samples.
Shore, S. K., L. A. Strauss, B. Considine, and A. Wallert, "The Technical Examination of a Pair of Embroidered Panels in the Collection of the J. Paul Getty Museum," The J. Paul Getty Museum Journal, Vol. 20, 1992.
ABSTRACT-Technical information is offered as a companion article to "Two Embroidered Hangings in the Style of Daniel Marot, 1680-1695" by Anne Ratzi-Kraatz in the same museum journal. It includes a description of the construction and execution of the panels. Examination of samples from both hangings has been conducted to identify the nature of the dyestuffs employed. Among the colorants were dyes from Genista tinctoria, Rhamnus cathartica, Caesalpina crista, Indigofera tinctoria, and Berberis vulgaris. Madder dyes were conspicuously absent from the samples taken for analysis. All of the technical evidence in the report supports the late seventeenth-century date of fabrication of both hangings. A more elaborate description of the analysis can be found in: Wallert, A., "Pair of embroidered bed hangings, analysis of dyestuffs," Getty Conservation Institute, Scientific Program-Museum Support Memorandum, 12.XI.1991, accession number: 85.DD.266.1, 2.
Stulik, D., and H. Florsheim, "Binding Media Identification in Painted Ethnographic Objects," Journal of the American Institute for Conservation, Vol. 31, Nº 3, Fall/Winter 1992, pp. 275-288.
ABSTRACT-This article describes a binding media identification procedure for the analysis of painted ethnographic objects. It is based on modified medical diagnostic and forensic science tests, and is designed to identify vegetable oils, lards, simple sugars, tree gums, starches, animal glues, casein, eggs, and blood in paint layer samples. Flow diagrams for individual tests are described as well as a binding media identification procedure and a general binding media identification flow chart.
Stulik, D., A. Parker, and D. Donahue, "Ultimate Challenge for Radiocarbon Dating: The Paint Layer," Paper presented to the Painting Speciality Group, 20th Annual Meeting, American Institute for Conservation, Buffalo, New York, June 2-7, 1992.
ABSTRACT-Radiocarbon dating techniques have been successfully used to date a number of archaeological artifacts. Application of the C-14 dating of easel and panel paintings is, so far, in its infancy and is limited to the dating of the wood or canvas support. A number of provenancing and authentication studies could not be finished conclusively because a possible forgery could be painted on an old or recycled supporting material. The solution to this type of problem is a direct dating of the paint layer. This is beyond the means of classical radiocarbon methods based on beta counting. A collaborative project between the Getty Conservation Institute and the Radiocarbon Laboratory at the University of Arizona at Tucson targeted on the application of accelerator mass spectrometry (AMS) in radiocarbon dating of microsamples from the paint layer. A new methodology uses sample sizes comparable to larger cross-sections taken regularly from museum objects by painting conservators. Special chemical and physical treatments have also been designed to clean the binding media samples of later contamination prior to dating. Application of the new methodology will be illustrated by dating the original paint layer and later repainting layers from Master Theodoric.c.Master Theodoric;'s Karlstein Castle series (1365-1367 c.e.).
Schilling, M. R., F. Preusser, and G. Gutnikov, "Analysis of High-Performance Liquid Chromatography Bonded Stationary Phases Using Thermo-gravimetry," Journal of Thermal Analysis, Vol. 38, 1992.
ABSTRACT-A thermogravimetric method was developed for determining the C-18 bonded phase content of reversed phase high performance liquid chromatographic stationary phases. The method yielded data that were comparable to the sum of carbon and hydrogen content. Excellent agreement between the two methods was achieved by heating the stationary phase samples to 150 °C in order to remove absorbed species prior to elemental analysis.
Schilling, M. R., F. Preusser, and G. Gutnikov, "Thermogravimetric Analysis of Calcium Montmorillonite Treated with Hexamethylene Diisocyanate," Journal of Thermal Analysis, Vol. 38, 1992, pp. 1635-1643.
ABSTRACT-The product of the reaction between calcium montmorillonite and hexamethylene diisocyanate in acetone, catalyzed with dibutyltin dilaurate, was studied by thermogravimetry to determine the amount of polymer produced. The method developed to determine polymer content in the clay possessed excellent accuracy and precision, and produced more consistent results than traditional gravimetric methods.
Striegel, M. F., and D. C. Stulik, "High Performance Thin Layer Chromatography for the Identification of Binding Media: Practical Techniques and Applications," Paper presented to the Paintings Group, American Institute for Conservation Meeting, Denver, Colorado, 1993.
ABSTRACT-The identification of the vehicle used to bind pigments on painted objects is valuable on both curatorial and conservation levels. While sophisticated analytical methods for the identification of binding media can be used in a research setting, conservators are often limited in the techniques available to them. A relatively simple, inexpensive method of identification, which provides high sensitivity and low detection limits for small samples (less than 100 µg), is therefore useful in the field of conservation. Organic materials which are often used as binders in paint include: proteins, sugars, drying oils, waxes, natural resins, and polymers. Conventional thin-layer chromatography, involving large saturation chambers and reagents in excess of 30 mL, has been used to qualitatively identify many of these organic binders. This research investigates recent advances in high performance thin-layer chromatography, including developments in sample preparation, sorbent layers, development chambers, and detection reagents. Use of computer technology in the evaluation of chromatograms is also studied. Practical techniques are reviewed.
Derrick, M., and D. Stulik, "Recent Advances in Identification of Binding Media in Paint Layers," Painting Specialty Group, 20th Annual Meeting, American Institute for Conservation, Buffalo, New York, June 2-7, 1992.
ABSTRACT-This presentation will focus on analytical methodologies used in binding media analysis. Several new methods developed in the course of the GCI Binding Media Project will be discussed from the point of view of a painting conservator. Application of the new methods will be illustrated by using several examples of medieval and modern paintings. An update on the Binding Media Collection introduced at the 1991 American Institute for Conservation meeting will also be provided.
Derrick, M. R., T. L. Kieslich, and D. C. Stulik, "Embedding Paint Cross-section Samples in Polyester Resins: Problems and Solutions," Paper presented to the Paintings Group, American Institute for Conservation Annual Meeting, Denver, Colorado, May 1993.
ABSTRACT-Polyester resins such as Bioplastic have been commonly used in art conservation for embedding paint cross-sections for analytical studies. The results from tests on several alternate embedding materials and procedures are presented in this paper. This includes an evaluation of other plastic embedding media such as acrylics, epoxies, and cyanoacrylates along with potential inorganic materials such as salt and malleable metals. Also included are the results for tests on barrier methods; this involves wrapping the sample in a material such as aluminum foil or mylar prior to embedding. The advantages and disadvantages for each method are discussed. Recommendations for use are based on the type of sample and its analysis requirements.
Derrick, M., "New Analytical Techniques for Use in the Conservation of Artistic and Historic Works of Art," SCALACS (Southern California American Chemical Society Newsletter), May 1993.
Derrick, M., E. Doehne, A. Parker, and D. C. Stulik, "New Analytical Techniques for Use in Conservation," Paper presented at the American Institute for Conservation Meeting, Research and Technical Studies Update Session, Denver, Colorado, May 1993.
ABSTRACT-Standard analytical equipment found in modern laboratories can answer questions most asked about samples. Specific questions occasionally arise that are outside the range of this equipment and result in modifications, new equipment designs, or just plain new approaches in analytical methodology. The paper offers examples of new techniques and equipment that offer significant applications and benefits to the art conservation field.
Derrick, M. R., D. C. Stulik, M. R. Schilling, C. M. Grzywacz, and M. F. Striegel, "Recent Advances in Binding Media Identification Using Multiple Analytical Techniques," Poster presented at the ICOM, Washington, D.C., August 1993.
ABSTRACT-Because paint binding media can be complex mixtures of materials and because their identification is often hindered by the presence of pigments and the effects of time, multiple analysis methods may be required for their complete characterization. This paper illustrates the complementary nature of several methods using samples obtained from paintings by Cenni di Francesco and Andrea Mantegna. It includes new aspects developed during the GCI Binding Media Project. A resource collection of reference materials and infrared spectra for binding media is also discussed.
Derrick, M. E., L. Souza, T. Kieslich, H. Florsheim, and D. Stulik, "Embedded Paint Cross-Section Samples in Polyester Resins: Problems and Solutions," Journal of the American Institute for Conservation, 33, 1994, pp. 227-245.
ABSTRACT- Polyester resins have been commonly used in art conservation for embedding paint cross sections prior to microscopic and analytical studies. These resins set rapidly without heat, are clear, polish readily, and microtome easily. While they work well for embedding most paint samples, they pose problems for some specific samples. The polyester embedding media have been found to dissolve wax, some organic colorants, and fresh natural resin layers in cross sections. The embedding resin also wicks into porous samples of low binder content. At times, infiltration can be desirable for its consolidating effects, but it can also interfere with the determination of the type of binder in the sample by producing blotchy, uneven staining results and by obstructing infrared analysis. Alternate embedding materials and procedures are discussed in this paper. One method to prevent the infiltration of embedding media is presented in which the samples are precoated with a thixotropic acrylic gel before embedding. Optimal microtoming techniques are also presented.
Grzywacz, C. M., "Identification of proteinaceous binding media in paintings by amino acid analysis using 9-fluorenylmethyl chloroformate derivatization and reversed-phase high-performance liquid chromatography," Journal of Chromatography A, Vol 676, 1994, pp. 177-183.
ABSTRACT-Identification of binding medium, the vehicle which adheres pigment particles to each other and to a backing or substrate, is important to both art conservators and curators. Proteinaceous binders such as egg, glue, and milk casein have been widely used by artists. A protocol for the identification of different proteinaceous binding media in paintings was developed using HPLC analysis with fluorescent detection of 9-fluorenylmethyl chloroformate (FMOC-CI) derivatives of amino acids.
A scheme based on peak area ratios of FMOC-amino acid derivatives was developed and successfully used on museum samples. The sample preparation techniques, identification scheme, and museum applications are discussed.
Schilling, M. R., and H. P. Khanjian, "Gas Chromatographic Investigations of Organic Materials in Art Objects: New Insights from a Traditional Technique," in Innovation et Technologie au Service du Patrimoine de l'Humanité, Symposium Preprints, Paris, 1996.
ABSTRACT-Gas chromatography has a long history of usage in conservation science. At he Getty Conservation Institute, research is being conducted to develop new gas chromatographic procedures for identification or organic binding media, and to assess the effects of physical aging and pigmentation on each medium.
In a procedure for identification of proteins involving ethyl chloroformate (ECF) derivatization of amino acids, it was discovered that alkyl-substituted and imino-substituted amino acids were least affected by pigment interferences and physical aging, hence they were termed "stable" amino acids. Although many different substances that contain amino acids may be present on art objects, most may be reliably identified on the basis of stable amino acid composition. Using correlation coefficients for data evaluation, a species of gum arabic was identified as the binding medium in the wall painting of the tomb of Nefertari located in Luxor, Egypt. Simple algebraic manipulation of stable amino acid compositions data made it possible to identify admixtures of egg tempera and animal glue in paint and gesso layers from the altarpiece of churches in Minas Gerais, Brazil.
Using a newly developed procedure that involved transesterification carried out in the presence of dimethoxypropane (DMP), derivatives of fatty acids and glycerol may be quantified in oil and tempera paint films. Because glycerol is present in each triglyceride molecule, and is reasonably stable, it provides a convenient internal reference for expressing the amounts of fatty acids detected in samples. It was discovered that saturated fatty acids, long believed to be stable, may in fact be depleted in oil paints by exposure to heat or light. Furthermore, azelaic acid was found to form in oil films during the early stages of drying., whereas other dicarboxylic acids form primarily after exposure to light. Results from testing of paint samples of Monet's "Waterlilies" at the Museum of Modern Art, New York, indicated the presence of walnut oil and poppy oil.
Simultaneous detection of proteins, oils, resins, and waxes present in a single microsample of paint may be accomplished by acid hydrolysis, followed by derivatization using N-methyl-N-(tert -butyldimethylsilyl)-trifluoroacetamide. (Tert -butyldimethylsilyl) derivatives of fatty acids, amino acids, glycerol, cholesterol, and other components are identified on the basis of retention times, using gas chromatography-mass spectrometry in selected ion monitoring mode. Test results for samples of paint taken from the 15th century Italian tempera painting, Dead Christ Supported by Angels, presently on loan to the Bonnefanten Museum in Maastricht, confirmed that proteinaceous and drying oil media were absent. In a separate carbohydrate analysis by gas chromatography, fruit gum was identified as the binding medium.
Schilling, M. R., H. P. Khanjian and L. A. Souza, "Gas Chromatographic Analysis of Amino Acids as Ethyl Chloroformate Derivatives. Part 1, Composition of Proteins Associated with Art Objects and Monuments," Journal of the American Institute for Conservation, 35, 1996, pp. 45-59.
ABSTRACT- Gas chromatography has long been used as a means of identifying proteins in acid hydrolysates of paint and adhesives on the basis of their amino acid composition. Existing procedures for amino acid derivatization can, however, take up to 4 hours per analysis, whereas a new procedure employed at the Getty Conservation Institute can be carried out in less than 20 minutes. This procedure involves the formation of N(O,S)-ethoxycarbonyl ethyl esters of amino acids using ethyl chloroformate and then a separation on an HP-INNOWAX capillary column. This procedure was employed to analyze samples from the binding media library at the Getty Conservation Institute, and amino acid compositions were tabulated for various proteins that could be used for identification purposes.
Schilling, M. R., and H. P. Khanjian, "Gas Chromatographic Analysis of Amino Acids as Ethyl Chloroformate Derivatives. Part 2, Effects of Pigments and Accelerated Aging on the Identification of Proteinaceous Binding Media," Journal of the American Institute for Conservation, 35, 1996, pp. 123-144.
ABSTRACT- Proteinaceous binding media present in paintings can be identified by gas chromatographic analysis of the ethyl chloroformate derivatives of amino acids. The effects of pigments on the amino acid composition data of hydrolyzed gelatin that were obtained by this method were studied. The method was also used to analyze glue and egg tempera paint films that were exposed to heat and light in order to accelerate the aging of the paints. Pigments and accelerated aging were found to affects the concentrations of all amino acids, although the concentrations of alkyl and imino-substituted amino acids were affected to a much smaller degree than others. Samples of grounds and paints that were removed from a number of paintings and painted objects were analyzed by this method. The proteins present in the samples were identified from the amino acid molar percentages by correlation to published amino acid composition data.
Schilling, M. R., and H. P. Khanjian, "Gas Chromatographic Analysis of Amino Acids as Ethyl Chloroformate Derivatives. III. Identification of Proteinaceous Binding Media by Interpretation of Amino Acid Composition Data," Scientific Examination of Works of Art, 11th Triennial Meeting Edinburgh, ICOM Committee for Conservation Preprints, September 1-6, 1996, pp. 211-219.
ABSTRACT-There has been considerable interest, of late, in the analysis and identification of proteins used as binding media and adhesives. The proteins most often used by artists include animal and fish glue, casein, glair and egg yolk. Other proteins may be present on objects, monuments and artifacts that can interfere with protein identification. Sources for these proteins include contamination from microbes, the use of saliva for cleaning painted surfaces, skin from handling of objects, and others. Additionally, some non-proteinaceous natural products that contain traces of amino acids may be mistaken for protein in an analysis. For instance, plant gums are composed of glycoproteins, substances in which amino acids are bonded to carbohydrate groups.
The intent of this paper is to describe a new mathematical procedure for evaluating amino acid composition data that permits the identification of proteins (and other substances that contain amino acids) in samples from art objects. Data from gas chromatography and high-performance liquid chromatography analyses of paint and gesso were evaluated in order to illustrate the utility of the procedure.
Schilling, M. R., and H. P. Khanjian, "Gas Chromatographic Determination of the Fatty Acid and Glycerol Content of Lipids. I. The Effects of Pigments and Aging on the Composition of Oil Paint," Scientific Examination of Works of Art, 11th Triennial Meeting Edinburgh, ICOM Committee for Conservation Preprints, September 1-6, 1996, pp. 220-227.
ABSTRACT-A gas chromatographic procedure for the analysis of fatty acids (as methyl esters) and glycerol (as isopropylidene glycerol) in oil paints is described. Molar ratios of selected fatty acids to the glycerol content were useful for characterizing lipids used in conservation. Evaluation of pigment interference's revealed that, of the pigments tested, only Paris blue, azurite and red lead had any measurable effect on the analytical results. Exposure of oil paint specimens to heat and light significantly increased the concentrations of most dicarboxylic fatty acids, whereas the amount of azelaic acid increased only slightly. Surprisingly, exposure to heat and light reduced the concentrations of saturated fatty acids in oil paints. Test results of samples from oil paintings were consistent with the trends established by the exposed oil paint specimens.
Schilling, M.R., and H.P. Khanjian, "Gas Chromatographic Investigations of Organic Materials in Art Objects: New Insights from a Traditional Technique Paper given ADMITECH meeting in Paris, 1997.
ABSTRACT--Gas chromatography has a long history of usage in conservation science. At the Getty Conservation Institute, research is being conducted to develop new gas chromatographic procedures for identification of organic binding media, and to assess the effects of physical aging and pigmentation on each medium.
In a procedure for identification of proteins involving ethyl chloroformate (ECF) derivatization of amino acids, it was discovered that alkyl-substituted and imino-substituted amino acids were least affected by pigment interferences and physical aging, hence they were termed "stable" amino acids. Although many different substances that contain amino acids may be present on art objects, most may be reliably identified on the basis of stable amino acid composition. Using correlation coefficients for data evaluation, a species of gum arabic was identified as the binding medium in the wall paintings of the tomb of Nefertari located in Luxor, Egypt. Simple algebraic manipulation of stable amino acid composition data made it possible to identify admixtures of egg tempera and animal glue in paint and gesso layers from the altarpieces of churches in Minas Gerais, Brazil.
Using a newly developed procedure that involves transesterification carried out in the presence of dimethoxypropane (DMP), derivatives of fatty acids and glycerol may be quantified in oil and tempera paint films. Because glycerol is present in each triglyceride molecule, and is reasonably stable, it provides a convenient internal reference for expressing the amounts of fatty acids detected in samples. It was discovered that saturated fatty acids, long believed to be stable, may in fact be depleted in oil paints by exposure to heat or light. Furthermore, azelaic acid was found to form in oil films during the early stages of drying, whereas other dicarboxylic acids form primarily after exposure to light. Results from testing of paint samples of Monet's 'Waterlilies' at the Museum of Modern Art, New York, indicated the presence of walnut oil and poppy oil.
Simultaneous detection of proteins, oils, resins, and waxes present in a single microsample of paint may be accomplished by acid hydrolysis, followed by derivatization using N-methyl-N-(tert -butyldimethylsilyl)-trifluoroacetamide. (Tert -butyldimethylsilyl) derivatives of fatty acids, amino acids, glycerol, cholesterol, and other components are identified on the basis of retention times, using gas chromatography-mass spectrometry in selected ion monitoring mode. Test results for samples of paint taken from a 15th century Italian tempera painting, Dead Christ Supported by Angels , presently on loan to the Bonnefanten Museum in Maastricht, confirmed that proteinaceous and drying oil media were absent. In a separate carbohydrate analysis by gas chromatography, fruit gum was identified as the binding medium.
Grzywacz, C.M., "Chromatography, Thin-Layer Chromatography and High-Performance Liquid Chromatography", chapters in GCI Analytical Techniques for Conservation, a course binder, July 1996.
Grzywacz, C.M., "Chromatography, Thin-Layer Chromatography and High-Performance Liquid Chromatography", chapters in GCI Analytical Techniques for Conservation, a course binder, July 1996.
Striegel, M. F., and J. Hill, "Thin-Layer Chromatography for Binding Media Analysis", Scientific Tools for Conservation Series, The Getty Conservation Institute, Los Angeles, California, ISBN 0-89236-390-8, 1996, 173 pages.
ABSTRACT- This book is the result of research and development efforts for "Methods in Scientific Examination of Works of Art: Thin-Layer Chromatography," a course held at the Getty Conservation Institute from 28 February to 4 March 1994. The course familiarized conservators and conservation scientists with thin-layer chromatography (TLC) as a method of binding media analysis.
The theory, practical techniques, and standard operating procedures for thin-layer chromatography as applied to conservation problems are detailed in this publication. It is divided into two parts: the handbook and the protocols. The handbook serves as a primer for the basic application of thin-layer chromatography to the analysis of binding media, adhesives, and coatings found on cultural artifacts. In the second part, the protocols provide step-by-step instructions for the laboratory procedures involved in typical analyses.