MAGNETIC SUSCEPTIBILITY THICKNESS CORRECTIONS FOR SMALL ARTEFACTS AND COMMENTS ON THE EFFECTS OF‘BACKGROUND’MATERIALS*

Correction factors for magnetic susceptibility measurements on thin (<c. 50 mm thick > artefacts have been determined experimentally for a KT‐5 Exploranium G S. instrument using prepared blocks of Whin Sill dolerite. The cor rection factor is large (> 1.4) for samples less than 10mm thick, and reduces to 1 01 for samples of 50mm thickness. Measurements on thin samples can also be affected by the backing or substrate material on which they are measured. ‘Background’material, for example, soil or plaster, can contribute significantly to recorded measurements on artefacts, particularly for thin artefacts with low susceptibilities     

EXPERIMENTAL EVALUATION OF SAMPLE‐EXTRACTION METHODS AND THE POTENTIAL FOR CONTAMINATION IN CERAMIC SPECIMENS*

Contamination of ceramic specimens resulting from sample‐preparation techniques has the ability to confound efforts of chemical characterization. Primary contamination, identified by significant concentrations of one or more elements, is easily identified. Secondary contamination, resulting from undetected elements influencing detected elements, is more difficult to identify. Evaluation of six powder‐extraction techniques identifies variable effects of contamination. Extraction by drilling carries the highest risk of contamination. The grinding of specimens with silicon‐carbide wheels may artificially deplete abundances by introducing Si and C. Grinding specimens in an agate mortar and pestle is found to be the technique least likely to result in contamination effects.