Colored grounds of gilt stucco surfaces as analyzed by a combined microscopic, spectroscopic and elemental analytical approach

A survey of gilts applied to stucco surfaces that specifically focuses on the compositions of their colored grounds is reported. Gilt samples of a common geographical (Lombardy in Italy) and temporal provenance (17th-18th century) were studied in the form of polished cross-sections by optical and electron microscopy (SEM-EDS), micro-Raman (?Raman) spectroscopy and Fourier-transform infrared microspectroscopy (?FTIR). Comparing samples with superimposed grounds and gilts enabled light to be shed on the choice of specific materials, their stratigraphic functions, decorative effects, and technological performances. Iron oxide pigments were found in the older grounds, sometimes in the presence of lead white (2PbCO3·Pb(OH)2) or minium (Pb3O4). In more recent grounds, chrome yellow (PbCrO4), chrome orange (PbCrO4·PbO), cinnabar (?-HgS) and barium white (BaSO4), invariably mixed with lead white, were encountered. Evidence for the use of organic mordants (colophony and wax, or siccative oil) was obtained by ?FTIR. This combined ?FTIR and ?Raman spectroscopic and elemental (SEM-EDS) analytical approach enhances knowledge of the composition of gold grounds, their variability and their chronological evolution.