Provenance Tracing Using Mother-of-Pearl and the Impact of Button Processing on the Material's Trace Elemental and Isotopic Compositions

Garment buttons and other artefacts incorporating mother-of-pearl (nacre) are significant items of material culture frequently found on archaeological sites and in museum collections. From around 1860 until the end of the Second World War, Australia was the foremost international source of mother-of-pearl for buttons, which were mechanically mass produced during that time. Since nacre formation is impacted by climate, water chemistry and other environmental factors at the time of shell formation, mother-of-pearl is potentially well suited to geochemical investigations of provenance. And yet, this avenue of inquiry, and the impact of button manufacturing on the compositional nature of mother-of-pearl, have received little attention to date. This study comprised stable carbon (δ13C) and oxygen (δ18O) isotope analysis of six mother-of-pearl samples from at least four different species sourced from the major pearling areas of Australia. It found oxygen isotope to be an effective marker in discriminating between most sample source locations, although some regions were not distinguishable. Additional and much higher density sampling and analysis of modern pearl shell might resolve this issue. The study also determined that mechanical processing during button manufacture has no significant impact on the trace element and isotope compositions of the mother-of-pearl. In doing so, it demonstrates the potential for source tracing mother-of-pearl material culture items to shed new light on the history of the pearling industry in Australia, one of the country’s most historically important maritime industries.