Characterisation of blue pigments from ceremonial objects of the Southern Highlands in Papua New Guinea using vibrational spectroscopy and X-ray diffraction

Amongst the mid-20th century cultural objects from Papua New Guinea (PNG) in a collection of the Art Gallery of New South Wales (AGNSW), Australia, is a number of items that are coloured with an unusual blue pigment. Many of the paints used for the ceremonial objects originating from the PNG Highlands employ a traditional red, yellow, white and black palette, so there is interest in the source of a blue pigment of apparent natural origin. For this investigation, infrared and Raman spectroscopies, in combination with a synchrotron x-ray diffraction study, were used to characterise blue pigments obtained from three objects in the AGNSW collection. The pigments were identified as vivianite-type minerals. The different shades of blue appearing in these objects were found to be associated with an early oxidation product of vivianite, rather than due to the presence of another mineral in the paints.