Experimental and analytical study of gold parting processes used in ancient times

This paper provides an overview of our previous experimentation on ancient gold refining methods and reports recent developments. The research project is based on the use of experimental archaeology and analytical chemistry applied to probable ancient gold assaying and refining methods, in light of archaeological evidence and ancient textual sources. The aim is to understand the processes and their outcomes, supporting archaeological interpretations regarding gold metallurgy and related chemical processes in ancient times. Previous experimentation was carried out using different combinations of man-made and natural compounds, belonging to the sulphate-halide group (i.e. misy or ios skolekos and salt) and the phyllosilicate-halide class (i.e. powdered brick and salt), tested and characterized in the reagent-product chains and thermodynamically interpreted. Experiments were also undertaken to understand multipurpose procedures such as the collection-scorification-cementation method for the parting of gangue, accessory minerals and metals (copper and silver) from gold by the combination of different processes conducted sequentially in the same crucible. Recent results have been obtained on the following topics: Misy from Cyprus is evaluated in ancient texts as to be of high quality, and the experiments carried out after an analytical appraisal of specific mineral compounds has allowed us to hypothesize a possible reason: compositions such as copiapite-rich gossans and Devil's Mud (sulphide-based composition), make the cements particularly effective in the purification process; The use of stibnite as a parting agent has also been tested and interpreted, thus adding this typeof sulphide process to the possible procedures used, as well as suggesting a thermo-chemical interpretation of cementation with Devil's Mud; Preliminary analytical results of trace element variation before and after cementation of alluvial gold are proposed as possible fingerprints of transient processes used in the processing of gold and the fabrication of gold artefacts; The multi-purpose usage of ancient cement recipes for the removal of surface oxidation during the production of gold artefacts and for depletion gilding.