The identification of fish oils in 20th century paints and paintings

Abstract

• Historic recipes show 19th-20th c. house paint manufacturers in the USA used fish oil. • Fish oil was cheaper than linseed oil and its presence in paints was not advertised. • GC–MS or HPLC-MS identify the unique fatty acid or TAGs profile of fish oil in paints. • Fish oil mixtures in some historic artists’ paints suggest adulteration. • Fish oil containing paints have been found in paintings by well-known artists. Vegetable oils such as linseed oil are commonly used in retail trade and artists’ oil and alkyd paints, but examination of historic trade literature from the 19 th and 20 th centuries suggests that paint manufacturers in the USA also used fish oils, especially from menhaden ( Brevoortia sp.). Gas chromatography-mass spectrometry and high-performance liquid chromatography-electrospray ionization quadrupole time-of-flight mass spectrometry of menhaden oil samples provided by Werner G Smith Inc., a modern company that supplies menhaden oil to the coatings industry, reveal a fatty acid profile distinct from that of vegetable oils. Menhaden oil has high levels of myristic acid, low levels of lauric acid and a high palmitic to stearic acid ratio and so is readily distinguished from vegetable oils by either of these methods. Historic paint recipes indicate that menhaden oils were often mixed with vegetable oils, so to establish detection limits we analyzed combinations of menhaden oil and either linseed, safflower or sunflower oils by GC–MS; the high levels of myristic acid remain characteristic in mixtures containing only 20% menhaden oil. A selection of historic artists’ paints pre-dating 1970 and paint samples taken from paintings dating from the 1950s and 1960s were analyzed to determine if fish oils could be detected. Fish oils may be present in historic artists’ paints, including those made by the Bocour Company, and in paintings by American artists Franz Kline, Barnett Newman, David Smith, and Andy Warhol. This is the first positive identification of fish oils in historic artists’ paints and 20 th century artworks.