Fire clay, analysis

Hedges, R.E.M. and McClennan, M. (1976). On the cation exchange capacity of fired clays and its effect on the chemical and radiometric analysis of pottery. Archaeometry 18 203-207. 

The fire clay for making the bricks which line the furnace, and which is generally found in the same mine with the ironstone, varies very considerably in composition in different localities, having properties more or less suitable for the purpose, according to the absence of oxides, and the quantity of silica and alumina. Tav-lok, in his analysis of the rocks of the coal-measures at the Hartley pit, gives the following... 

NAA study of approximately 170 sherds from the site was undertaken to answer this question. This totally included 117 sherds and three fired clay samples from Pinson Mounds, 39 sherds from nearby contemporary sites, five samples of clay sources in the area, and six sherds from a Hopewell site in Georgia. Nineteen of the sherds from Pinson appeared to be nonlocal in style and temper. The research reactor at the University of Missouri was used to irradiate the samples and instruments measured the abundance of 33 elements in ppm in the pottery. Statistical analysis of the data from the NAA study was then undertaken. The authors of this study, Mainfort and colleagues, removed a number of samples with unusually high or low data values (known as outliers) from their study, arguing that these outliers can cause samples to appear more similar. 

These bricks may therefore be called nlicecus oj etone bricks, and will no doubt prove admirably adapted for the construction of many kinds of chemical furnaces. A red fire-brick is likewise manufactured at Windsor, the analysis of the clay from which it is prepared being... 

Tablets come into a somewhat different category. All that is ever wanted of them is their inscriptions and it is common practice to fire tablets so that they can be handled indefinitely. Should only clay be wanted for analysis an unscribed section can be set aside and left unfired. Any treatment to be given to tablets in the field depends on whether there is a kiln on the site or not and, if not, on how desperate the epigraphist is to read them on the spot.

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