Gypsum mortars from a twelfth-century church in Wiślica, Poland

Abstract

AbstractArchaeological excavations in Wiślica (Poland) exposed the stone foundations of a little twelfth-century church which formed the crypt under a later, gothic collegiate church. Gypsum mortar was used to bind the stone blocks making up the foundations and for the floor of the crypt. The central part of this floor is decorated with engraved designs, the . grooves of which are filled with a pigmented mortar. After studying the mortars using electron and optical microscopy, X-ray diffraction and differential thermal analysis, the mortar binding the blocks and that filling the grooves were both found to contain about 87% gypsum and 2·6% calcite, while the respective contents for the mortar of the engraved floor were 92% and 1·1%. Gypsum calcined at high temperatures, known as ‘estrich gypsum’ (anhydrous gypsum plaster—mineralogically anhydrite), was used. Two kinds of calcination process were employed, resulting in two types of mortar: one, coarse-grained and fastsetting, was used to bind the blocks and...