A sample of burnt clay (SBC 1), recovered from context 80, c. 0.5 m deep in the central pit of the umber ciicle, was examined by thermoluminescence (TL). The clay was expected to be either Bronze Age or Iron Age in date, being associated either with the timber circle or with the Iron Age metal working in the top of the central pit.

The TL dating method measures the time that has elapsed since the heating of the material (which zeroes the TL signal). The measurement consists of firstly a determination of the radiation dose received by the sample since its heating (through the examination of its TL) and secondly an assessment of the rate at which the radiation dose was received (carried out by radioactivity measurements). Further descriptions of the method are given by Aitken (1985) and Zimmerman (1971).

The outer 2 mm or more of the sample were cut away to remove those pans that had been exposed to light and to the alpha and beta activity of the surrounding sediment The interior piece was crushed, and fine grains of 2-10 mu were separated by suspension in dilute hydrochloric acid. The grains were then washed in water, methanol and acetone before deposition onto aluminium discs.