Synthetic organic pigments (SOP) that have been manufactured and subsequently removed from manufacture are referred to as historical SOP. A class of azo-containing SOPs, Naphthol AS pigments were first synthesized in 1892, and first patented in 1909. Though many are still commercially manufactured, certain of these are not available and therefore, there is no modern analytical data. Thus if their presence is suspected, for example in artwork, it would be difficult if not impossible to identify them. Without their identity, the art history of the object would be less comprehensive and deep, and display and conservation decisions would be less informed. With their identity, a specific time range of use can be inferred. We have investigated the literature and have targeted a series of historical Napthol AS (Fig. 1) pigments (PR7, PR10, PR11, PR18, PR19). These compounds can be thought of as a 2-hydroxy-3-napthoic acid reacted to form an arylamide at the acid site and an aryl-azo at the 1-site. Synthesis from commercially available chemicals will be described. Analysis of the product pigments by FT-IR, Raman, mass spectrometry (GC/MS, MALDI) and NMR will be presented. The utility of this method to assist in art conservation and provide opportunities in undergraduate research will be highlighted.

Historical organic pigments: The challenge and opportunity of the nearly forgotten

251st National Meeting (2016)

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