Colorimetric and structural characterization of cinnabar from classical localities

Cinnabar use in painting is historically documented from ancient times. The pigment, also known as vermilion, had its maximum spread in Roman times, as many Latin authors report. However, only a few information can be found about cinnabar extraction deposits, except for the Iberian and Colchis regions. Recent experimental techniques have tried to deepen and solve the problem, unfortunately with no possibility to distinguish vermilion from far localities. The aim of the present work is to better characterize cinnabar from different quarries by colorimetric and X-ray diffraction analysis, to finally organize the collected data in a provenance data-base. Colorimetric analysis show that cinnabar has a typical reflectance curve with a minimum at the lowest wavelengths, a maximum at the highest wavelength and a distinctive wavelength corresponding to 600 nm. The values of maximal reflectance allow samples assignment to one of three color varietis. Moreover, CIELab parameters can characterize cinnabar from different localities taking into account the a* values. X-ray powder diffraction was used on the same sample set as a preliminary test to underline structural variation connected to cinnabar provenance. Volume data were extrapolated and compared on the basis of cinnabar thermal behaviour. They show that relevant differences exist in terms of unit cell volume, also within samples from the same district.