An analytical investigation of a unique medieval wood sculpture and its monochrome surface layer

Medieval wood sculptures form an important part of our cultural heritage. Their preservation, restoration and material investigations usually result in a very demanding task, which leads, however, to understanding of the historical techniques used in the medieval art workshop. The restoration of the statue of Seated Virgin Mary (1475–1480), recently attributed to the Master of the Kefermarkt Altarpiece, the National Gallery in Prague, revealed beneath the thick layer of the modern polychrome a very rare preserved original surface finish consisting of a thin monochrome glaze that was directly applied to the wood, in German specialised literature known as Holzsichtigkeit . The identification of the organic materials of the thin painting layers on original artworks is always very challenging. The monochrome red-brownish glaze was confirmed by micro-optical analyses in ultraviolet light. The layer was then analysed by means of micro-chemical test for the presence of saccharides and subsequently investigated by gas chromatography–mass spectrometry to detect particular binding medium. According to the results it occurred that storax was plausibly present. This research and identification of the surface finish of the Seated Virgin Mary sculpture open new possibilities for the interpretation and analyses of similar monochrome glaze layers of the Late Gothic carvings.