Thermal analysis of Romanian ancient ceramics

Abstract

The present work is focused on thermoanalyt- ical investigations as thermogravimetric analysis (TG) and derivative thermal analysis (DTG), applied for the char- acterization of some samples collected from archaeological sites (Brasov and Trofeum Traiani) located in different regions of Romania. New informations derived about ceramic technologies concerning raw materials and binding materials (mineralogical components) have been obtained. All these experimental results have been correlated with related techniques as X-ray diffraction (XRD), energy- dispersive X-ray fluorescence (EDXRF) and inductively coupled plasma—atomic emission spectrometry (ICP- AES). By progressive heating in static air atmosphere and in the temperature range of 20-800 � C, all investigated materials exhibit three main successive processes, associ- ated with the dehydration and thermo-oxidative degrada- tions. The rate of the first thermooxidative process, temperatures corresponding to the maximum rate of the second thermooxidative process and shrinkage temperature were associated with the damage of the investigated materials due to environmental impact. Heating also affects the contact between the fine-sized clay matrix and mineral clast fragments, appearing in reaction rims, sometimes showing newly formed phases. The temperature at which ancient ceramics and pottery were fired varies over a wide range (600-800 � C) depending on the type of clay used, although firing temperatures not above 30-400 � C have also been suggested. Clay minerals, as the main material for production of ceramics and pottery, show some char- acteristic reactions (dehydroxylation, decomposition, transformation) in the course of firing (heating effects) and several thermoanalytical criteria can be used for recon- struction of former production conditions.