Potential and limitations of adhesive identification on museum curated metal objects

In Europe, adhesives were produced and employed from the Middle Palaeolithic onwards. In the earlier periods, adhesives were used predominantly for hafting tools and weapons, but their functionality evolved with the advent of ceramic technologies, with use widening to pottery repair and ornamentation. Limited attention has been directed towards their application in metalwork. It is unclear whether the scarcity of adhesives described in association with metal is due to preservation factors, such as corrosion-related issues, or to a research emphasis on other materials associated with metalwork such as coral, amber, and glass. To address this issue, we conducted chemical analyses including gas chromatography – mass spectrometry on 18 adhesive residues present on 15 objects from France and England dated from the mid first millennium BCE to the first century CE. These artefacts include jewellery, vessels, harness fittings and weaponry components. Our findings suggest that a range of adhesives were employed in assembling and applying decoration to diverse types of metal objects. These include birch tar and conifer resins, also bitumen and possibly beeswax, which have not been reported before. However, the application of waxes in past conservation practices introduces challenges that can potentially constrain the interpretation of molecular analyses. Our results have implications for the understanding of the adhesive technologies, and illustrate the potential of identifying adhesives linked to metal ornamentation. They further demonstrate the widening application of long-established adhesive technologies within the framework of increasingly complex craft specialisms.