Characterisation of the physico-chemical and optical properties of Australian native plant exudates for a simple method to determine archaeological resins and gums

Abstract

Plant exudates, specifically resins and gums, have been used for millennia for a variety of purposes. This research characterises Australian plant exudates to allow simple procedures to be used for the characterisation and determination of plant exudates in residues from archaeological and anthropological artefacts. Various physico-chemical and optical properties of exudates were investigated including colour, density, solubility, melting point, UV luminescence, isotropy and pleochroism. This research showed that solubility and UV luminescence provided a very useful combination in determining the plant source of various exudates. It was also determined that solubility in a specific sequence of solvents also provided an extremely simple and efficient diagnostic key to screen residues that may contain a plant exudate. To validate the procedure, a set of artefacts were examined using this screening method that were previously identified using FTIR and GC-MS. This testing can be non-destructive and can be performed as micro-chemical techniques under a microscope or using simple portable equipment, that can easily be used by archaeologists in the field.