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.

The Raman spectra of approximately 20 reference samples of cobalt-based green and violet artists' pigments of various provenance (present day manufactory, historical reference pigments and samples from a contemporary artist's studio) were acquired to assist in the identification of unknown cobalt-based pigments in works by Pablo Picasso (1881-1973) and Jasper Johns (b. 1930. Specifically, Raman spectra were obtained for various cobalt titanate greens (Co 2 TiO 4 ), highlighting variability in peak positions because of ionic substitutions in the spinel structures of such pigments. The Raman spectra of the cobalt violet pigments magnesium cobalt arsenate (Mg x Co 3-x (AsO 4 ) 2 ) and hydrated forms, ammonium cobalt phosphate hydrate (NH 4 CoPO 4 *H 2 O), and anhydrous cobalt phosphate, Co 3 (PO 4 ) 2 were also recorded; some of which are presented here for the first time. Fourier Transform Infrared spectroscopy (FTIR), x-ray fluorescence spectrometry (XRF) and x-ray diffraction (XRD) were employed to confirm the composition of the reference materials. An optimal technique to characterize microscopic cross sections from the studied artworks is Raman microscopy, which can also provide valuable information on the hydration states of the examined phases. The multi-analytical methodology allowed the identification of the unknown green pigment used by Jasper Johns as cobalt titanate green (C.I. PG 50); representing the first documented occurrence of this pigment in the palette of a renowned contemporary artist. Both magnesium cobalt arsenate (in anhydrous and hydrated forms) and anhydrous cobalt phosphate were identified in the Picasso painting.This research advances the knowledge of 20th century synthetic inorganic pigments used by artists and documents their usage in actual works of art.

This study reports the multi-analytical investigation of ready-mixed house paints used by artists such as Pablo Picasso (1881-1973) in the first half of the twentieth century. The pigment composition of paint swatches on four historic paint sample cards from the Art Institute of Chicago reference collection was characterized by thorough screening using Fourier transform infrared (FT-IR) and X-ray fluorescence (XRF) spectroscopies, followed by Raman spectroscopy when necessary. Spectroscopic investigations highlighted the dominance of zinc-based whites, the consistent choice of particular pigments or their mixtures, as well as the avoidance of others to achieve the various hues on the sample cards. Notable findings included the documentation of strong spectroscopic signatures of metal soaps. Given the similarities in composition of early twentieth century artists' and house paints, the results indicate that the identification of house paints in works by Pablo Picasso and others must be based on a combination of parameters rather than the detection of a single chemical marker. Results have been applied to the case study of Picasso's 1935 sculpture Figure (AIC 1988.428), which incorporates direct evidence of the use of house paint by the artist.

Georges Seurat first employed his divisionist painting technique, commonly called pointillism, on