Arlen Heginbotham

The Use of Immunofluorescence Microscopy and Enzyme-Linked Immunosorbent Assayas Complementary Techniques for Protein Identification in Artists' Materials

Abstract Antibody-based immunological approaches to identifying protein-based materials offer several advantages over traditional methods of analyzing works of art. These techniques are able to easily distinguish different protein types (e.g., collagen vs. ovalbumin vs. casein), and also to determine unambiguously the biological source of the protein (e.g., bovine collagen vs. rabbit collagen vs. sheep collagen). The technique of enzyme-linked immunosorbent assay is highly sensitive, with detection limits below one nanogram, and is relatively simple and cost-effective. In addition, immunofluorescence microscopy offers the possibility of spatially resolving target proteins in embedded cross sections. This paper presents a case study in which these complementary methods were successfullyemployed for the identification of egg albumin in the analysis of an important 17th-century French cabinet by André-Charles Boulle in the collection of the J. Paul Getty Museum. The authors suggest that enzyme-linked immunosorbent assay and immunofluorescence microscopy have the potential to become routine analytical tools in conservation science laboratories.

Beyond the basics: A systematic approach for comprehensive analysis of organic materials in Asian lacquers

Identification of organic materials in Asian lacquers presents many challenges due to their complex formulations and the limited solubility of the main component, which is catechol-rich sap from three species of Anacardiaceae trees that crosslinks to form a hard film. Pyrolysis-gas chromatography–mass spectrometry with thermally assisted hydrolysis and methylation using tetramethylammonium hydroxide (THM-Py-GC–MS) has been shown to produce a wide range of marker compounds useful for identifying the catechol components and lacquer additives such as drying oils, natural resins, proteins, starch, and colorants. However, interpreting the test results is quite challenging because of the sheer number of compounds produced by pyrolysis and the wide range of materials that have been used in traditional Asian lacquer formulations. An expert system developed by scientists at the Getty Conservation Institute and conservators at the J. Paul Getty Museum for a workshop entitled ‘Recent Advances In Characterizing Asian Lacquers’ (RAdICAL) utilizes software tools to overcome challenges in data analysis and marker compound interpretation, making it possible for even relative newcomers to Py-GC–MS to identify materials in lacquered objects systematically. Automated Mass spectral Deconvolution and Identification System (AMDIS), a freeware program developed by the National Institute of Standards and Technology (NIST), systematizes GC–MS data analysis by rapidly deconvoluting chromatograms, identifying individual peaks, and then searching the results against a user library of marker compounds, producing a simple report that lists the names, retention indices, and peak areas for all the compounds identified in the sample. The authors have produced a custom RAdICAL compound library, compiled from in-house studies of reference samples made from mixtures of raw or processed lacquer mixed with additives, and supplemented by published work from other researchers. The lists include numerous oxidation products of the alkyl- and alkenyl-substituted catechols, and alkyl- and alkenyl-substituted benzenes in the tree saps identified in studies of aged lacquer replicas, many of which have diagnostic purposes. A specialized Excel workbook developed for RAdICAL can import the AMDIS report, organize the marker compound results by class of artists’ materials, and perform automatic calculations to display sorted information for each material in specialized diagnostic graphs. Expert knowledge relating raw materials to their associated marker compounds, obtained from in-house research, publications and personal communications has been embedded into the individual Excel worksheets. This aids users of the workbook in verifying the presence or absence of materials in their lacquer samples, based on the marker compound distributions. All of the final results are presented in a pre-formatted comprehensive analytical report. Extensive lists of analytical data for marker compounds from the major classes of organic additives used in Asian lacquer formulations provide researchers the information needed to identify these markers in unknown lacquer samples. As other researchers contribute marker compound information for further lacquer materials and the knowledge for interpreting them, the capabilities of the RAdICAL expert system will continue to expand.

Materials and techniques of gilding on a suite of French eighteenth-century chairs

Abstract This paper describes the technical study of a suite of French Rococo chairs at the J. Paul Getty Museum with original eighteenth-century gilding preserved under layers of restoration. A variety of analytical methods was employed to identify and characterize the materials of the preparatory layers and gold alloys including optical microscopy, digital image analysis, polarized light microscopy, scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDX), Raman spectroscopy, and X-ray diffraction (XRD). The materials and techniques were compared with descriptions of French eighteenth-century gilding practices in contemporary artists’ treatises. Both burnished and unburnished original gilding, employing distinctive techniques, were found. The study was particularly focused on the gold alloys and the support layer for burnished gilding, a mixture known as assiette in French and as bole in English. In addition to the original gilded surface, several subsequent campaigns of gilding executed with the same eighteenth-century techniques were present on the chairs and visually indistinguishable from the original gilding. The alloy of the gold leaf used in each campaign was characterized through quantitative SEM-EDX via a calibration generated from the SEM-EDX data from gold standards. Characterization of the gold alloys proved to be a vital tool for the interpretation of the layer structure and identification of original gilding.

Some observations on the composition of Chinese lacquer

This paper summarizes the various information that has been gathered in recent years at the J. Paul Getty Museum and Getty Conservation Institute with regard to the organic constituents of Chinese lacquer formulations. While this summary of materials is by no means comprehensive or complete, it captures the current state of the authors’ knowledge, with the information itself and the bibliography intended to serve as a useful foundation from which further research may proceed. Considerable advances have been made in the last decade in the technique of pyrolysis-gas chromatography–mass spectrometry with thermally assisted hydrolysis and methylation using tetramethylammonium hydroxide and in subsequent data interpretation methodologies. These have dramatically improved the sensitivity and specificity of organic analysis. Perhaps equally important, these methodologies are allowing researchers to collaborate much more effectively and to share results that are truly comparable and reproducible. As more researchers participate and collaborate, and as more results are aggregated into shared databases, significant new insights into the methods and materials of Chinese lacquer are sure to follow.

AN EVALUATION OF FOUR BARRIER-COATING AND EPOXY COMBINATIONS IN THE STRUCTURAL REPAIR OF WOODEN OBJECTS

Abstract Barrier coatings are widely used in conservation to add a measure of reversibility to an otherwise irreversible adhesive bond. Barrier materials are applied as thin films to mating surfaces prior to application of a primary (irreversible) adhesive. Subsequently, if reversal is required, the barrier layer can be softened or dissolved, releasing the bonded joint. This investigation was undertaken to determine the suitability of two synthetic resins for use as barrier layers in the bonding of wood with epoxy. The two materials in question, Paraloid B-72 and Paraloid B-67, were chosen because of their potential to be practically reversible in low-polarity solvents. The two polymers were compared, as barrier materials, to two proven barrier coatings, hide glue and Butvar B-98, by measuring their strength in shear according to ASTM D905-98. Investigations were also undertaken to determine the amount of time necessary for barrier layers to dry prior to application of epoxy. Finally the practical reversibility of the barrier coatings was empirically evaluated. Paraloid B-72 was found to be a suitable barrier material in all respects, while Paraloid B-67 failed both strength and reversibility tests.

Chinese lacquer: Much more than Chinese lacquer

A significant portion of Asian lacquer collections in today’s western museums was originally made in China specifically for export to European markets. The J. Paul Getty Museum’s collection includes pieces of French furniture dating to the mid-eighteenth century that incorporate panels of Chinese export lacquer as part of their surface decoration, an early eighteenth-century inkstand thought to be of Ryukyuan origin (76.DI.12), an eighteenth-century secretaire (65.DA.3), and an eighteenth-century black lacquered cupboard (78.DA.119). In a systematic technical study of these lacquered objects, analysis of the organic constituents in individual lacquer layers was carried out using pyrolysis – gas chromatography – mass spectrometry with tetramethylammonium hydroxide derivatization (THM‒ Py‒GC‒MS) [1–3]. Additionally, the presence of protein, oil, and starch within the layer structure of lacquer cross sections was visualized with both visible and blue light illumination after treatment with selected stains used in histochemical protocols [4]. As the research progressed, objects from other museum collections were studied for comparative purposes in order to gain a broader understanding of temporal and geographic trends in Chinese lacquer formulation. It had been assumed that all Chinese qi lacquerware was made from urushiol, which is the exudate of Toxicodendron verniciflua trees that grow throughout specific regions of China, Japan and Korea. However, this study revealed that Chinese export lacquered objects were formulated with laccol, which is the exudate from Toxicodendron succedaneum. 現今西方博物館收藏的亞洲漆器,有大部份是中國

Bending Asian lacquer in eighteenth-century Paris: New discoveries

Rococo furniture decorated with fragments of Asian lacquer was highly fashionable in eighteenth-century France. The furnitures curvilinear designs forced cabinetmakers to manipulate flat lacquer e...