A systematic analysis of red lake pigments in French Impressionist and Post‐Impressionist paintings by surface‐enhanced Raman spectroscopy (SERS)

Abstract

The Art Institute of Chicago (AIC) owns one of the largest and very finest collections of 19th century French Impressionist and Post‐Impressionist paintings in the world. While the palette of the Impressionists has been extensively characterized for what concerns both traditional and innovative inorganic pigments, to date, the identification of the red organic lakes – widely used for their intense, brilliant color – has posed an analytical challenge. In this work, firstly, surface‐enhanced Raman spectroscopy has been applied to the analysis of red lake paint reconstructions prepared according to 19th century historical recipes. Results demonstrated that dye identification can be successfully accomplished on Lee–Meisel colloids after hydrolysis with hydrofluoric acid, even when inorganic pigments, extenders, ground materials or binding media are associated with the red lake in the sample analyzed. Subsequently, the same protocol was used to examine samples from Manet, Pissarro, Renoir, Monet and Gauguin paintings in the AIC collection. Results showed the predominant use of madder and cochineal lakes, sometimes in combination, thus greatly enhancing our knowledge of the Impressionist usage of different types of red lakes. Copyright © 2014 John Wiley & Sons, Ltd.