Estimation of Firing Temperature and Compositional Variability of Archaeological Pottery by Differential Scanning Calori
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Estimation of Firing Temperature and Compositional Variability of Archaeological Pottery by Differential Scanning Calorimetry A. Giordana,a E. Peacock,b M. McCarthy,a K.Guilbeau,c P. Jacobs,b J.D. Seger,b and W.G. Ramsey,d a Diagnostic Instrumentation and Analysis Laboratory (DIAL) at Mississippi State University, 205 Research Blvd., Starkville, MS 39759 b Cobb Institute of Archaeology at Mississippi State University (MSU), P.O.Box AR, Mississippi State, MS 39762 c Now at the College of Veterinary Medicine of MSU, Starkville, MS 39759 d Now at Earthstone, LTD, 555 Republic Dr. Ste 440, Plano, TX 75074. ABSTRACT Digital Scanning Calorimetry (DSC), a thermal characterization technique, can be used to rapidly obtain a rough upper estimate of the firing temperature of archaeological pottery as well as an indication of its composition. The technique involves heating a small sample (10-20 mg) of ground ceramic above the vitrification temperature, cooling and reheating. The curves of the two heating cycles are then compared. The validity of the technique was evaluated by a blind test in which 35 tiles fired at different temperatures were analyzed without knowing their firing point, and by analysis of archaeological pottery samples assumed to be local or imported based upon stylistic criteria. INTRODUCTION The use of materials characterization techniques to investigate the composition and firing of archaeological pottery has become common in recent years.1,2,3,4 In this paper we describe the results of the application of a thermal characterization technique, Differential Scanning Calorimetry (DSC), in estimating the firing temperature of ceramics.5 Use of the technique in determining the provenience of archaeological pottery and other possible applications is also discussed. DSC is a well-established materials characterization technique6 that allows detection of the changes in the heat capacity of a material as a function of temperature. The changes in heat capacity are related to changes in the structure or composition of the material. Some examples of such changes are softening, melting, crystalline phase transitions, and evaporation or decomposition of components. DSC analysis is destructive, but only a small amount of material – as low as 10 milligrams – is required. The purpose of the studies described in this paper was: 1) to determine the effectiveness of DSC analysis in determining an upper value for the firing temperature of archaeological pottery; and 2) to establish whether the technique could be used to differentiate between local and imported materials. The method we have developed consists of repeated thermal cycling in the DSC furnace of a powdered sample of the analyzed sherd or tile. Depending on the temperature reached by the clay, water is driven out, carbon dioxide is released by the decomposition of carbonates, and crystalline transitions such as the α -β quartz transition at 573°C occur. Most transitions are
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irreversible, i.e., they will not “undo” when the sample has cooled down an
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