Sanguine Paint: Production,Characterization, and Adhesion to the Glass Substrate

ABSTRACT

For centuries, the only painting materials used in stained-glass production were grisaille and yellow (silver) stain. At the end of the fifteenth century, stained-glass painters began to use a new material, sanguine. This paint is mainly produced with iron oxide particles, usually haematite, and allowed to obtain a colour that can vary from yellowish to brownish-red due to the nature and particle size of the iron oxide. A translucent sanguine was mostly applied as flesh and hair colour, with an opaque sanguine used for drapery, architectural motifs, and heraldry. The main goal of this study is to investigate the relationship between historic sources on the preparation and use of sanguine from the fifteenth to the nineteenth centuries and the evolution evidenced in the recipes regarding the production method. Representative recipes from several centuries (sixteenth to nineteenth centuries) were selected and reproduced for this study. These reconstructions were thoroughly characterized using X-ray powder diffraction, optical microscopy (OM), and fibre optic reflectance spectroscopy (FORS). The OM and FORS data were correlated with historic sanguine paints applied on historic stained-glass. The similarities and differences between historic and reconstructed paints are presented. The study of reconstructed sanguine’s adhesion to glass using cross-cut testing was also performed, revealing that the adhesion is strongly influenced, not only by the binder, but also by the composition and morphology of the sanguine paint.