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Raman analysis of South African pottery (shards) dating from the 13th and 14th centuries reveals that the potters used a variety of clays and fired their wares at less than 800 Celsius using open fires rather than kilns. Such details could only be unearthed without damaging the artefacts using this powerful spectroscopic technique. Chemists M.A. Legodi and Danita de Waal of the University of Pretoria in South Africa examined samples from four archaeological sites - Rooiwal, Lydenburg, Makahane, and Graskop using normal dispersive Raman spectroscopy. They complemented this technique with X-ray fluorescence, X-ray diffraction and Fourier transform infrared spectroscopy. Despite the fact that Raman scattering from clays is usually poor, the team were able to identify 13 chemical phases in the representative samples from pottery discovered in the 1930s. Lydenburg, Makahane and Graskop shards contained kaolin (an aluminium silicate), illite (a potassium aluminium silicate), feldspar (potassium and sodium aluminium silicate), quartz (alpha silica), hematite (alpha iron oxide), montmorillonite (a magnesium silicon aluminium salt), calcium silicates, including gypsum, and calcium carbonates (putatively calcite). The team also found amorphous carbon phosphates in the Lydenburg, Rooiwal, and Makahane shards, although rutile (titania) was present only in the Makahane shard. The basic conclusion of the study is that South African potters from this period used various clay mixes as raw materials. The structure of the fired clay indicates that it was fired at less than 800 Celsius, which the researchers say suggests it was hardened in an open fire rather than a kiln. "The identification of so many chemical components in the low temperature fired clay products demonstrates the high sensitivity and applicability of Raman spectroscopy to these type of samples," say the researchers. They add that, " Due to its ability to detect various chemical species in low temperature fired clay products (as shown in this study), Raman spectroscopy can be useful in determining the raw materials used, processing conditions and discrimination based on unique chemical compounds." Related links:
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De Waal uses Raman to unearth pottery shard secrets |
