Determination of the composition of the ancientcolour pigments used by artists in Singida and Kondoa-Irangi rock paintings by XRF.

In central Tanzania there is a large number of ancient rock paintings which have been drawn mostly on shelter rocks. The colours used in the paintings are white, red, yellow and black. The pigments and the material used by ancient artist in making these colours were not well known. This study aimed in determining the composition of the colours and suggests the pigments and materials used in making the colours. Two independent techniques namely WDXRF and TXRF were used to determine the composition while CHN elemental analyzer was used to determine the presence and amount of organic carbon in the samples. Samples used in WDXRF were of two types, paint sample which contain both colour pigment and rock on which the paintings were drawn and the rock sample which is the rock only, the results from rock samples were compared to the results of the analysis of paint samples. In TXRF, samples were obtained from a very soft scratch on paintings in order to obtain only colour pigments; this was done in order to minimize the effect of geochemical background. The results from TXRF concur with the results from WDXRF. The red colour was found to be from red ochre (Fe2O3), yellow colour was found to be from either Titanium yellow or yellow ochre (Fe2O3 X nH2O), white colour from chalk (CaCO3) and gypsum (CaSO4X2H2O) while black colour was found to be from Ivory black (C + Ca3(PO4)2). All pigments were found to contain some amount of organic carbon in different concentrations. Organic carbon in the pigment is related to the use of organic binders during preparation of the colours. Furthermore some pigments were found to contain large amount of calcium and phosphorus which suggest the usage of bones in preparation of those pigments especially in white and black colours.