Identification of causes of degradation of Gothic ceramic tiles by thermal analyses

Thermal analyses are suitable methods when studying not only nowadays, but also archaeological ceramic materials. In this case, they were used to study the mineralogical composition and the ageing process of a collection of fragments of Gothic mosaic tiles which were found during archaeological research of Břevnov Benedictine Monastery in Prague. The ceramic bodies of the tiles were differently coloured and showed different degrees of degradation. The ageing process of low-fired ceramics is accompanied by irreversible moisture expansion of a ceramic body which can lead to its degradation. The expansion of ceramic bodies of selected tiles was evaluated by the modified dilatation method. Thermal analyses with the combination of other methods (XRF, XRD and IR) and induced hydrothermal treatment proved the presence of clays in raw materials and helped to identify the causes of different degrees of degradation of the studied tiles.