Identifying Pigment Mixtures in Art Using SERS: A Treatment Flowchart Approach.

A novel treatment flowchart approach for surface-enhanced Raman scattering (SERS) is used to identify both blue and yellow organic pigments in a single microscopic sample from a series of reference oil paints as well as an actual 18th century oil painting. In particular, several treatment strategies using acids and solvents are integrated into a specific flowchart designed to enable the minimally invasive identification of unknown blue (i.e., indigo, Prussian blue) and yellow organic (i.e., Reseda lake, Stil de Grain, gamboge) pigments in one sample. We demonstrate the first successful identification of a yellow lake pigment in a historic painting using SERS as well as the utility of our treatment flowchart approach for identifying pigments of varying resonance conditions, surface affinities, and treatment requirements in a single microscopic sample from a historic oil painting.