The analysis of artists’ paints, hierarchically complex materials typically composed of binder, pigments, fillers, and other additives is a challenging, multiscale problem. Techniques as simple as visual observation under a visible light stereomicroscope and as complex as high resolution nanoprobe SR- X-ray fluorescence (XRF) mapping are deployed by museum scientists to answer questions about composition, stability, manufacturing technology, and even the artist’s intention.

I will present select case studies drawn from the masterpieces of the collection of the Art Institute of Chicago including the investigation of the color darkening of selected brushstrokes of Georges Seurat’s A Sunday on La Grande Jatte-1884 , which was noted as early as 1892, but never successfully explained until the present study. Electron energy loss spectroscopy (EELS) measurements determined the presence of altered species in the form of Cr(III) compounds and di-chromate ions (Cr (VI)). Laboratory simulations demonstrated that the equilibrium between chromate and di-chromate ions is reversible within the paint film and that the orange di-chromate ions can be transformed back into bright yellow chromates by exposure to highly alkaline gases. This would obviously not be an acceptable conservation treatment, and instead, digital simulations of the original colors have been created.

Furthermore, an extensive study on the technology and characteristics of Ripolin, a popular brand of non-artists’ French house paint used extensively by Pablo Picasso and some of his contemporaries will be presented. The talk will describe in detail work undertaken at the nanoprobe, seeking to obtain highly spatially resolved, highly sensitive mapping of metal impurities (Pb, Cd, Fe, and other metals) in submicron particles of zinc oxide pigments used in these early 20th century enamel paints. The chemical characterization of paints at the nanoscale opens the path to a better understanding of their provenance, fabrication and chemical reactivity.

Argonne Physics Division Colloquium Schedule