Investigation of a Roman age “bulk pigment” found in Vicenza Original Research Article

This work is devoted to the study of a violet-pink material, which was found in a fairly good quantity during an excavation in Vicenza (Contrà Pedemuro S. Biagio), both on the bottom of a black varnished goblet and in a red purified small amphora with black traces of a titulus pictus (inscription) on its neck. The techniques used were optical microscopy, scanning electron microscopy (SEM), equipped with an energy dispersive microanalysis detector, X-ray powder diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy and cyclic voltammetry (CV). The results demonstrated that the sample was not a mixture of natural pigments, but a synthetic product deriving from alunite (KAl(SO4)2·12H2O) dissolved or suspended in water, from which white aluminium hydroxide was precipitated. An alkaline madder root extract solution was probably added to aluminium hydroxide to obtain the “Garance Lacquer”. The colour of this lacquer varied depending on the pH of the extract. The bulk pigment could have been used in the decoration of objects or, most probably, attributed to pharmacopoeia products for the treatment of blood diseases or as skin astringent.