Kaolinite-alunite association in late Gothic white grounds from Slovakia: A local peculiarity in painting technology

摘要

In European Gothic paintings, the use of materials other than calcium carbonates (chalk) or calcium sulphates (gypsum) in painting preparations was rare. Therefore, alternatively used materials, such as, e.g., white clays, can be seen as peculiarities, which correspond to the local availability or artist's preference. In this study white chalk-based grounds from masterpieces attributed to the workshop of Master Paul from Levaa, Slovakia, were investigated. It was motivated by the assumption of restorers that Master Paul complemented the chalk ground by more malleable white clay to achieve a very fine modelling of his polychrome statues. The results were compared with other artworks, where the use of white clays in grounds was previously indicated, and with reference samples of kaolin from Central-European sources. It was found that detailed microanalysis of the white earths in paintings leads to distinguishing of regional provenances. While in Czech paintings, either from Gothic or Baroque periods, residual kaolins from West-Bohemian deposits were identified, in the late Gothic Slovak paintings white earths came from hydrothermal kaolin deposits situated, most probably, in Tokaj Mountains, Hungary. Here presented fmding is probably the first ever evidence of natural alunite and hydrothermal kaolinite in painted artworks, where they were applied as white pigments.