Analysis of ochres from Clearwell Caves: the role of particle size in determining colour
Marshall, L. J. R., Williams, J. R., Almond, M. J., Atkinson, S. D. M., Cook, S. R., Matthews, W. and Mortimore, J. L. (2005) Analysis of ochres from Clearwell Caves: the role of particle size in determining colour. Spectrochimica Acta Part a-Molecular and Biomolecular Spectroscopy, 61 (1-2). pp. 233-241. ISSN 1386-1425
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To link to this article DOI: 10.1016/j.saa.2004.03.041
Three ochre samples (A (orange-red in colour), B (red) and C (purple)) from Clearwell Caves, (Gloucestershire, UK) have been examined using an integrated analytical methodology based on the techniques of IR and diffuse reflectance UV-visible-NIR spectroscopy, X-ray diffraction, elemental analysis by ICP-AES and particle size analysis. It is shown that the chromophore in each case is haematite. The differences in colour may be accounted for by (i) different mineralogical and chemical composition in the case of the orange ochre, where hi,,her levels of dolomite and copper are seen and (ii) an unusual particle size distribution in the case of the purple ochre. When the purple ochre was ground to give the same particle size distribution as the red ochre then the colours of the two samples became indistinguishable. An analysis has now been completed of a range of ochre samples with colours from yellow to purple from the important site of Clearwell Caves. (C) 2004 Elsevier B.V. All rights reserved.