AIC's 45th Annual Meeting

Proteins from a variety of sources, such egg, milk, hide and fish, are ubiquitous components of artworks and cultural objects. It has long been recognized that detecting the presence of and determining the nature of proteins is an important part of conservation. Knowing the materials used gives important insights into the choices and intentions of the artist; knowing the materials can aid in determining authenticity and guide future generations in understanding and accurately recreating the culture of their ancestors; knowing the materials is essential toward directing conservation, storage and display. Historically, the detection and identification of proteins in artworks has been accomplished by a variety of methods including amino acid analysis (AAA), FTIR, Raman, immunological methods (ELISA), GC, GCMS. PyGC, and HPLC. Each method has its strengths and weaknesses. For example, FTIR and Raman may be the least invasive methods but in most cases can offer little more than verification of the presence of protein and perhaps broadly classify its origin. AAA requires relatively large samples but can determine protein presence and generally discriminate among broad classes of proteins found in artworks. ELISA offers high sensitivity and small sample requirements but can suffer from the lack of relevant antibodies. The relatively recent migration of LCMSMS and PMF into the conservation laboratory offers enhanced sensitivity and specificity and significantly advances the conservator's ability to identify proteins with high sensitivity and specificity. Despite increased levels of sensitivity of newer methods, protein determination still requires that samples be taken from the object for analysis. Although some artworks offer acceptable "sampling opportunities,” such as paint on a folded canvas edge or areas of prior damage, in many cases such opportunities are absent, and the conservator must decide whether the potential gain in information outweighs the need to alter the object or painting, however slightly. This presentation will discuss two minimally invasive methods developed for sampling solids and surfaces to obtain material sufficient for subsequent protein analysis by PMF or LCMSMS. The first method, the use of 2–3 mm3 polymer eraser cubes, is an extension of the method (triboelectric extraction) described by Fiddyment, et al.1 for noninvasive sampling of velum. This adaption of that method is best suited for sampling friable surfaces and coatings thereon, where minuet amounts of surface and/or coating material can be abraded loose and adhered electrostatically to the cube. The second method utilizes polishing films of fine alumina or diamond particles and is best suited for hard surfaces, such as ivory, bone, paint and photographs, which might not be sufficiently abraded by the eraser. Although technically invasive, both methods offer an option for obtaining samples with nearly unnoticeable effect on the surface. In each case, the sampling device, eraser cube or polishing film, is placed directly into the digestion buffer for subsequent enzymatic cleavage for protein analysis by PMF or LCMSMS. Examples of the use of both methods will be shown for analyzing samples from parchment, ivory, bone, hide, photo prints and painted surfaces. 1 www.pnas.org/cgi/doi/10.1073/pnas.1512264112