The characterisation of pigments used in X-ray rock art at Dalakngalarr 1, central-western Arnhem Land

The chemistry of pigments used to create rock art at a rock shelter in northern Australia has characterised so as to gain a better understanding of the origins of the colours used. The site, Dalakngalarr 1, located in Jawoyn Country in Arnhem Land contains hundreds of paintings in various colours and styles. Striking and well-preserved X-ray images were painted across the site using ochre pigments that contain an iron oxide colourant mixed with clay to produce yellow, red and a distinctive purple colour. Infrared and Raman microscopy were used to confirm that the yellow pigment colouration is due to the presence of goethite. Both the red and purple pigments were shown to contain haematite, but there are microstructural differences between the two that account for the differences in the observed colour. Optical microscopy and scanning electron microscopy also demonstrate differences in the morphologies of the red and purple pigments. The purple pigment was found to a have a pure haematite structure, which is proposed to result from heating of the pigment source.