Species identification of ivory and bone museum objects using minimally invasive proteomics.

Ivory is a highly prized material in many cultures since it can be carved into intricate designs and have a highly polished surface. Due to its popularity, the animals from which ivory can be sourced are under threat of extinction. Identification of ivory species is not only important for CITES compliance, it can also provide information about the context in which a work was created. Here, we have developed a minimally invasive workflow to remove minimal amounts of material from precious objects and, using high-resolution mass spectrometry-based proteomics, identified the taxonomy of ivory and bone objects from The Metropolitan Museum of Art collection dating from as early as 4000 B.C. We built a proteomic database of underrepresented species based on exemplars from the American Museum of Natural History, and proposed alternative data analysis workflows for samples containing inconsistently preserved organic material. This application demonstrates extensive ivory species identification using proteomics to unlock sequence uncertainties, e.g., Leu/Ile discrimination.

Hydrogen­deuterium exchange mass spectrometry to study interactions and conformational changes of proteins in paints.

Little is known about structural alterations of proteins within the polymeric films of paints. For the first time, hydrogen­deuterium exchange mass spectrometry (HDX-MS) was implemented to explore the conformational alterations of proteins resulting from their interaction with inorganic pigments within the early stages of the paint film formation. Intact protein analysis and bottom-up electrospray-ionisation mass spectrometry strategies combined with progressively increasing deuterium incubation times were used to compare the protein structures of the model protein hen egg-white lysozyme (HEWL) extracted from newly dried non-pigmented films and newly dried films made from a freshly made mixture of HEWL with lead white pigment (2PbCO3 Pb(OH)2). The action of other pigments was also investigated, expanding the HDX study with a global approach to paint models of HEWL mixed with zinc white (ZnO), cinnabar (HgS) and red lead (Pb3O4) pigments. The results show structural modifications of HEWL induced by the interaction with the pigment metal ions during the paint formulation after drying and prior to ageing. Both the charge distribution of HEWL proteoforms, its oxidation rate and its deuterium absorption rate, were influenced by the pigment type, providing the first insights into the correlation of pigment type/metal cation to specific chemistries related to protein stability.

A pioneer of acrylic painting: new insights into Carmen Herrera's studio practice.

Carmen Herrera, born on May 30th, 1915, is a Cuban American abstract minimalist artist, whose first solo show was held at the Whitney Museum of American Art, New York, in 2016-2017. On this occasion, a scientific study of five paintings from the artist's time in Paris (1948-1953) revealed her pioneering use of solvent-based acrylic paints in post-war Europe. This article presents a second phase of research into Herrera's work aiming to shed light on her studio practice and ascertain the possible presence of other early acrylic paints in her pre-1963 artistic production. A selection of four paintings, namely Iberia #25 (1948), Iberic (1949), Flights of Colors #16 (1949), and Early Dynasty (1953), was subjected to an analytical campaign that relied on both non-invasive and micro-invasive techniques. Results confirmed the use of both oil and solvent-based acrylic paints, supporting our primary research and uncovering the first-known occurrence of acrylic binders in Herrera's Iberia #25. In all cases, the ground layer consists of a mixture of titanium white in its tetragonal form of rutile, anhydrite, and talc, while the color palette was found to be based on both traditional and modern pigments. In most areas, several paint layers appeared to be overlaid on top of one another, revealing a creative process that developed through subsequent compositions. Remnants of earlier paint layers, which appeared to have been scraped off before new ones were applied, were observed directly above the ground in some of the samples examined. In addition, Iberia #25 and Iberic, with analogous geometric and chromatic schemes, underwent technical imaging, which exposed pencil lines and notes underneath the paint layers likely indicative of the intended design and polychromy. Besides corroborating a major alteration in the current scholarship on the availability and use of acrylic-based artists' paints in post-war Europe, this research provides new insights into Herrera's materials, techniques, and studio practice. In addition, the results of this scientific study assisted the development of a suitable treatment plan for Iberic in preparation for its display in The Metropolitan Museum of Art's galleries as part of the museum's 150th anniversary exhibition Making The Met, 1870-2020. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1186/s40494-021-00603-3.

Luminescence of coprecipitated titanium white pigments: Implications for dating modern art.

Material analysis of cultural artifacts can uncover aspects of the creative process and help determine the origin and authenticity of works of art. Technical studies on abstract expressionist paintings revealed a luminescence signature from titanium white paints whose pigments were manufactured by coprecipitation with calcium or barium sulfate. We propose that trace neodymium present in some ilmenite (FeTiO3) ores can be trapped in the alkaline earth sulfate during coprecipitation, generating a luminescent marker characteristic of the ore and process. We show that the luminescence is linked to a specific ilmenite source used in historic TITANOX pigments, is not present in pigments produced by more advanced chemistries, and provides dating information. Facile Raman-based detection of this luminescence, along with characteristic peaks of rutile, anatase, calcium sulfate, or barium sulfate, can identify the type of titanium white pigment and narrow its manufacture date range.

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).

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.

An improved method of protein localization in artworks through SERS nanotag-complexed antibodies.

There are several analytical techniques currently in use in conservation science to identify proteins in artworks. However, as is often the case, the determination of the exact location of a protein in a complex layer structure is challenging due to difficulty in separating layers. Localization of the protein in a cross-section has been demonstrated through attenuated total reflectance-Fourier transform infrared mapping and imaging as well as chemiluminescent and fluorescent-labeled antibodies; however, these techniques either require expensive instrumental setups or produce results that can be challenging to interpret. This paper will present research using surface-enhanced Raman scattering (SERS) nanotags complexed to secondary antibodies in conjunction with primary antibodies for the localization of ovalbumin, collagen, and casein in cross-sections from replicas and artworks containing avian egg, animal glue, or casein binders. The advantages of this technique over the others are (1) the detection method is a Raman microscope, equipment found in several museum laboratories; (2) the distinctive SERS signal from the nanotag increases the detection limit of the protein and decreases the interference from other colorants present in the cross-section layers; and finally, (3) the large (120 nm) SERS-labeled antibodies do not appear to penetrate into the cross-section, eliminating the risk of spurious signal and misidentification. Any agglomerations due to surface texture are clearly visible under normal illumination and can be avoided easily during analysis or removed with a light polish. This technique not only allows protein localization in multilayered samples while preserving the stratigraphic information but also retains the protein specificity of the antibody approach.