Julie Arslanoglu

Immunology and art: using antibody-based techniques to identify proteins and gums in artworks.

Our diverse world cultural heritage encompasses a vast range of objects, from fi ne art to monumental cultural heritage sites, which represent not only artistic developments but also power, politics and commerce. They are combinations of materials and cultural infl uences that vary over time and according to style, taste, region and artist or workshop. The careful study of how an artwork is made is critical to its preservation: correct identifi cation of materials can guide conservators in treatments but also can direct curators and conservators in display and storage strategies. This identifi cation can also help reveal working practices of the artist, studio or guild: for example, the use of egg tempera, egg mixed with oil or only oil as a binding media in paintings marks a distinct alteration in working practice in Italy in the mid to late 15th century (Dunkerton 1996; Higgitt and White 2005). Furthermore, the identifi cation can also give insight into the trade customs of a town or region and, in some cases, may facilitate authenticating, dating, and determining the regional provenance of an object. For example there are pigments that were only used over certain time periods or became commonly used only later in the 19th century: thus their presence, in conjunction with other supporting evidence, can aid in determining the likely date of origin for an artwork. Scientifi c examination is critical in providing this knowledge and is an essential component in modern technical studies of artworks and cultural heritage. Throughout history a great variety of natural products have been used in art and one of the most common applications of organic materials has been as binding media, adhesives and varnishes1. Mixed with pigments they form the basis for paints (binding media), as adhesives they allow solid joints in furniture, and as varnishes they supply protective coatings for paintings, wood, and other decorative surfaces. Animal and plant materials used in art as binding media and adhesives include oils, waxes, resins, gums, mucilages and proteins. Eggs, milk, and animal glues (made from bones, skin, or fi sh bladders) composed primarily of the proteins ovalbumin, casein, and collagen — can not only be found in artworks but are also used to conserve art. Plant gums such as gum tragacanth2, cherry gum, and gum arabic, known as polysaccharides, have been used mainly as binding media for water soluble paint. Analysing the binding media and adhesives on artworks presents unique challenges. The natural materials, which can be used individually or in combination, are actually complex chemical mixtures whose composition can alter over time due to human intervention (e.g. conservation treatments), environmental conditions (heat, light, humidity, biodeterioration), and chemical interactions between the components of the mixture.In addition, the organic material can be encased in a complex solid matrix, such as pigments, and its concentration in that matrix tends to be very low. Furthermore, the original organic binder or adhesive may itself be a mixture (multiple protein sources or oil and protein mixture, for example) or may have become so via the migration of materials, for example between layers of paint during conservation treatment with adhesives or the application of coatings. And fi nally, that a sample of the artwork is required in order to identify proteins and gums dictates that the analytical techniques be

Development and application of an ELISA method for the analysis of protein-based binding media of artworks

ELISA has been used extensively in scientific research and medical diagnostics since its invention in the 1960s. The application of ELISA to identify proteinaceous materials used in works from cultural heritage is a recent development and presents an important area of further investigation. This study introduces an optimized ELISA with a horse radish peroxidase (HRP) reporting system to identify select proteins in the adhesives and binders used in artworks. The described methodology is successfully applied to samples obtained from three different artworks from the Metropolitan Museum of Art. Furthermore, these experiments use protein quantitation to study the impact of specific pigments/binder combinations on the antigen detection by commercial antibodies. Our results suggest that the aging of specific pigment/binder combinations could impact the ELISA detection of proteins in artworks.

“Picasso in The Metropolitan Museum of Art”: An Investigation of Materials and Techniques

Abstract The 2010 exhibition “Picasso in The Metropolitan Museum of Art” presented the unparalleled opportunity to examine the working methods and materials of Pablo Picassos paintings in the museums collection, 34 works in total, covering a span of over 60 years. All paintings were comprehensively examined and studied using infrared reflectography and x-ray radiography. The paintings with paint surfaces that visually presented qualities associated with alkyd, enamel, or house paints were analyzed. Four paintings presenting such significant characteristics emerged from the group and are the focus of this study. Pigment and binding media analyses indicated the possible use of non-traditional artists paints but not necessarily house, alkyd, or enamel paints. Picassos infinite creativity was reflected in his experimental nature with materials. Specifically, his manipulation and alteration of the oil medium, which directly impacted the appearance and handling properties of the paint, must be taken into account. Ultimately, the results of this study illustrate the difficulty in identifying house, boat, or other non-traditional artists paints by visual examination alone and the challenges of their analytical characterization. Our analyses showed the presence of traditional artists materials of the time period but did not definitively identify chemical markers of house or other non-traditional artists paints.

Influence of pigments and protein aging on protein identification in historically representative casein-based paints using enzyme-linked immunosorbent assay

A systematic study on the influence of pigments and sample aging on casein identification was performed on 30 reconstructed paints. The protein in all the paints was extracted into solution for analysis. The amount of protein that can be retrieved for solution-based analysis in each of the reconstructed paints was studied with a well-developed NanoOrange method before and after artificial aging. The results showed that in the paints with calcium phosphate (in bone black) and copper carbonate, hydroxide, or acetate (in verdigris and azurite), the amount of protein that can be retrieved for liquid-phase analysis is much smaller than the other paints, indicating that the protein degradation was accelerated significantly in those paints. Carbon (in vine black), calcium carbonate (in natural chalk), and calcium sulfate (terra alba gypsum and ground alabaster) did not affect much the amount of protein that can be retrieved in the paints compared to non-pigmented binder, meaning that the protein degradation rate was not affected much by those pigments. Artificial aging was observed to decrease the amount of retrievable protein in all the reconstructed paints that were studied. The enzyme-linked immunosorbent assay (ELISA) method was applied to the 28 reconstructed paints (except two verdigris paints) to assess the protein identification. The ELISA responses from the different paints were compared at fixed protein concentrations. Natural chalk, bone black, raw sienna, stack lead white, and cochineal red-violet lake had the lowest ELISA signal in this study, which indicated that the binding sites (epitopes) on the target protein in these paints are likely to deteriorate more than those in the other paints. Artificial aging did not influence the ELISA response as much as the pigments when the protein concentration was kept the same for the paints that were studied.

Plant gum identification in historic artworks

We describe an integrated and straightforward new analytical protocol that identifies plant gums from various sample sources including cultural heritage. Our approach is based on the identification of saccharidic fingerprints using mass spectrometry following controlled enzymatic hydrolysis. We developed an enzyme cocktail suitable for plant gums of unknown composition. Distinctive MS profiles of gums such as arabic, cherry and locust-bean gums were successfully identified. A wide range of oligosaccharidic combinations of pentose, hexose, deoxyhexose and hexuronic acid were accurately identified in gum arabic whereas cherry and locust bean gums showed respectively PentxHexy and Hexn profiles. Optimized for low sample quantities, the analytical protocol was successfully applied to contemporary and historic samples including ‘Colour Box Charles Roberson & Co’ dating 1870s and drawings from the American painter Arthur Dove (1880–1946). This is the first time that a gum is accurately identified in a cultural heritage sample using structural information. Furthermore, this methodology is applicable to other domains (food, cosmetic, pharmaceutical, biomedical).

Distinguishing manufacturing practices for titanium white pigments: New Raman markers for dating commercial oil-based paints

The invention of titanium white pigments revolutionized the paint industry in the 20th century. Nontoxic, relatively inexpensive, moderately fast-drying, and with high covering power, titanium white was everything that zinc and lead white pigments were not. Although initially slow to be adopted as an artists’ material, titanium dioxide-containing paints were ubiquitous by the latter half of the century, so the presence of titanium white in a modern painting might seem to provide little dating or material information. However, changes in the technologies of pigment production have resulted in several shifts in the nature of the pigments used. The first titanium white pigment produced in the USA was the anatase crystal form co-precipitated onto barium sulfate (1916), a type of pigment also termed ‘composite’. The anatase form co-precipitated onto calcium sulfate was introduced by 1925, and pure anatase itself was widely available by 1927. The rutile form, with a higher refractive index and greater coloring power, was more difficult to manufacture; the co-precipitated forms of this species were not introduced until 1941, and the pure species became available in 1957. The rutile–barium sulfate co-precipitate was supposedly phased out in the late 1940s while production of the calcium sulfate co-precipitate continued until the 1970s. Therefore, determination of the crystal form of the titanium dioxide, which is a task easily accomplished by Raman spectroscopy, can provide some dating information. However, co-detection of titanium dioxide and calcium (or barium) sulfate in a sample does not necessarily indicate that a co-precipitated pigment is present, as both calcium sulfate and barium sulfate are commonly used fillers/extenders which can be mechanically added to titanium dioxide. Scanning electron microscopy coupled with energy dispersive X-ray spectroscopy of individual pigment grains may provide evidence of co-precipitated pigments rather than mere mechanical mixtures, but this is a time-consuming and laborious process that precludes facile identification of these species. Recent technical studies on paintings by abstract expressionists Kline and Newman dating from the 1950s to 1960s in the collections of the Museum of Fine Arts and the Menil Collection, Houston, USA, and the Metropolitan Museum of Art, New York, USA, revealed a Raman fluorescence signature in certain titanium white paints. In these paints a series of broad peaks at ∼1195, 1280, 1370, 1475, 1575, and 1660 cm (Fig. 1) is detectable only when using a 785 nm laser (not 514 or 633 nm lasers). These peaks are assigned to fluorescence from trace amounts of iron incorporated into the crystal structures of the pigment, which occurs only in co-precipitated anatase and rutile pigments produced by the sulfate process (Fig. 2) (Smith, 2006). The presence or absence of this fluorescence along with characteristic Raman peaks of rutile or anatase titanium dioxide, and calcium or barium sulfate, allows determination of the crystal form and whether the pigment is a co-precipitate. This precise identification of the type of titanium white pigment permits a narrowing of the date range of paint manufacture from a single analytical measurement. A small survey of 38 paintings largely from the Menil collection and dating from 1940 to 1985 has found co-precipitated pigments in 10 of the works, with the rutile-calcium sulfate species being most common. All of the works date from 1950 to 1967 and include not only paintings by Kline, Newman, and other well-known artists including Warhol and Rauschenberg, but also more obscure artists such as Walter Egel Kuhlman and William Christenberry. The former was active in California and the latter in Tennessee when the works in question were painted, indicating that the co-precipitated pigments are not Correspondence to: Corina E. Rogge, The Museum of Fine Arts Houston and The Menil Collection, Houston, TX, USA. Email: crogge@mfah.org

Cut from the Same Cloth: A Technical Comparison of Jackson Pollock’s Pasiphaë and Mural

This essay takes Pollock’s painting Pasiphaë as a comparative for Mural. Both paintings were begun in 1943 and were significantly larger in scale than the artist’s previous works. Using technical analysis to study Pasiphaë, Duvernois, Arslanoglu, and Centeno explore the similarities and differences between Pollock’s painting materials and techniques in Pasiphaë and Mural, ultimately drawing two conclusions: that the canvases for these paintings were cut from the same roll, and that Pollock began painting both canvases not with dark outlines but rather with fluid brush applications of lighter pigments.