Characterising the X-ray painting at Dalakngalarr rock shelters

The three colour types used in the X-ray paintings at Dalakngalarr 1 have been characterised. Goethite was identified as the main component of the yellow pigment. Haematite has been shown to be responsible for the red and purple colourations. The variation in the observed colour of red versus purple is proposed to be due to the presence of an impurity in the form of haematite contained in the red pigment. This addition is not present in the purple pigment, which shows a pure haematite structure. A form of heat treatment of an ochre source, whether deliberate or unintentional, is the proposed mechanism for the formation of the unusually lustrous purple pigment. Heating of ochre pigments can change the crystal structure of the haematite component and the particle size, which manifests itself in a colour change.