Combination of non-invasive and micro-destructive methods used in the investigation of tin-relief patterns on a Bohemian Late Gothic altarpiece

Abstract

This paper aims to summarise the results obtained during the investigation of a lavishly decorated Bohemian medieval altarpiece, which depicts the legend of St. Catherine of Alexandria, and is situated in the Church of St. Catherine in Chrudim, Eastern Bohemia. This altarpiece belongs to a unique group of high-quality medieval altarpieces which have been preserved in Chrudim. The research focused above all on the late-medieval decorative technique known as pressed brocade. The relief applications were coloured in order to imitate the luxury textile with the greatest possible precision. This process also included gilding and a coloured finish of the relief surface. The research team investigated the decorative patterns, imprints of the moulds used, the quality of the execution, the chemical composition of the filler material and, the way in which the tin relief was produced and applied onto the painted surface. The attention was paid also to the final gilding and glazing. The material investigation included a non-invasive X-ray fluorescence analysis of carefully selected samples prepared as cross-sections. The filler material underneath the tin relief were analysed using optical microscopy, micro-Raman spectroscopy, ATR-FTIR spectroscopy and scanning electron microscopy with X-ray microanalysis. Gas chromatography/mass spectrometry was then employed to identify the presence of lipid, resin and protein binding media in the composition of the filler material. The experimental data obtained during the research serves as the basis for more general conclusions concerning workshop practices in the late Middle Ages. The results will also be used to plan the complex restoration of the altarpiece.