Hidden Pigments In Portrait Miniatures - Purple Of Cassius

The palettes used by miniature portrait artists included various inorganic and organic pigments. The first miniatures were executed on stretched vellum (parchment); later on, the variability of supports increased (paper, glass, metal, ivory). Watercolour and gouache were the most common techniques. In addition to pigments that did not differ in any way from those used by painters of larger paintings, there were also rarely used pigments, typically appearing just in the miniatures. In the literature, silver white or Purple of Cassius are mentioned, but there is a lack of their clear evidence in actual paintings. In this study, Purple of Cassius was identified in one French portrait miniature from the 19th century due to increased concentration of gold in purple shades of the painting. In addition, the production of Purple of Cassius was replicated combining historical recipes and classical laboratory methods. The applied procedure included dilution of a gold bar in aqua regia and reduction with powdered tin. The prepared pigment was characterized by confocal microscopy and scanning transmission electron microscopy (STEM) with energy-dispersive X-ray spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS) detectors in the bright field mode (BF).