AIC's 42nd Annual Meeting

A novel, two-step procedure using for quantifying the percentage of unbound fatty acids (free fatty acids plus pigment soaps and salts) and total fatty acids of oil paints by gas chromatography/mass spectrometry (GC/MS) was developed. The following samples were analyzed in this study: Bocour Bellini oil tube paints; Winsor & Newton student-quality oil paints (1953-1992); paints made at the Museum Conservation Institute (MCI) with cold-pressed linseed oil (1992-1999); Winsor and Newton artists-grade oil paints (1990-1999); Duro artists’ oil paints (1960s); tube paints collected from among Clyfford Still’s studio materials which included tube paints from Bellini, Weber and Grumbacher (assumed to pre-date 1980); Clyfford Still paintings (1940-1970); and various mural and panel paintings. Marker compounds for specific drying oils were detected in Clyfford Still’s studio tube paints. All of the Bellini paints and the Weber paint sample contained 12-hydroxystearate, which is found in castor oil-derived products. The Talens tube paint contained ricinoleic acid, which is also present in castor oil, but is also used in some modern synthetic pigments. P/S values were less than 1 in all of the Grumbacher Permanent Oil Color artist’s-grade tube paints, which is unusually low

In this study, the percent fatty acids and percent hydrolysis of oil paint is reported for Bellini oil paints, Winsor & Newton student-quality oil paints that are sensitive to water, Duro oil paints and tube paints from Clyfford Still’s studio, as well as several other oil paintings including: Virgin and Saints by Ubaldo Gandolfi (1758), Annunciation by Bartolomeo Cesi (1515), Waterlillies by Monet (1914-26) and Mural by Jackson Pollock (1943). The results revealed that water sensitive modern oil paints have very little if any free fatty acids, possibly due to the presence of driers or a chemical modification. Some of the other tube paints analyzed in this study had zero percent free fatty acids, regardless of the age of the paint, and water sensitivity. Several paintings from various mural and panel paintings from the 16th to 18th century (Italian) as well as modern paintings were analyzed for free fatty acid profiles and were compared to reference data from tubes and handmade paints. The data presented here supplements the traditional fatty acid ratios for oil identification by adding an additional level of characterization from the free fatty acid profiles.