Investigating the history of prehistoric glues by gas chromatography–mass spectrometry

Abstract

Although organic materials are very sensitive to biochemical alteration processes, they may be preserved for millennia in various archaeological contexts. Remains of adhesives made during prehistory were discovered at different sites, in the form of residues adhering to flint tools and ceramic vessels or as free lumps in sediment. To characterise the natural substances exploited for adhesive production during late prehistory, we undertook GC and GC/MS analysis of 90 samples from 8 sites dating from the Neolithic to Iron Age periods. This paper discusses our approach to the study of organic adhesives preserved in archaeological contexts, with a particular focus on the presentation of the various categories of organic adhesives that we analysed and the choice of chromatographic conditions adapted to the specificity of such samples. The results obtained show that birch bark tar, a triterpenoid adhesive made by destructive distillation of white birch bark, was predominantly used during the neolithic period even though other materials such as various barks or organic fossil substance were also used. During the Bronze and Iron ages, which follow the Neolithic period, adhesive production is evolving through the expansion of the range of the natural substances used (identification of diterpenoid pine resin) and the addition of beeswax as a plasticiser to birch bark tar. By combining chromatographic analysis and archaeological data, it was thus possible to follow the evolution of adhesive making at the end of prehistory, testifying to the inventiveness of the craftsmen whatever the period considered.

A New Approach for the Characterization of Organic Residues from Stone Tools Using GC×GC-TOFMS

“…The resin samples yielded the most complex volatile signature of all sample types analyzed. Resin is an important substance in archaeological research as it has been used during prehistory as an adhesive to haft stone tools [9,30]. Hafting is considered an invention that revolutionized stone tool use [30,31] and that necessitated abstract thought and planning [9,32].…”

“…Resin is an important substance in archaeological research as it has been used during prehistory as an adhesive to haft stone tools [9,30]. Hafting is considered an invention that revolutionized stone tool use [30,31] and that necessitated abstract thought and planning [9,32]. Therefore, being able to understand the mode of preparation allows an understanding of the cognitive and technical capabilities of their makers [33].…”

“…Finally, an ideal method of analysis should be non-destructive in order to preserve the sample if other testing is required. Despite being a particularly challenging area of research, GC-MS has been employed successfully in numerous archaeological investigations including, but not limited to, the analysis of smoking pipe residue from ancient burials [6], ceramics [7], plasters [7], resins [2,5,[8][9][10], and resin additives, such as beeswax [9,11].…”

“…The history of the sample only adds to this complexity, leading to the degradation of certain components and the potential for contaminant compounds to become present over time. A number of studies using one-dimensional gas chromatography (1D GC) have demonstrated the complexity of a vast range of modern reference and archaeological samples [1,3,9,[12][13][14]. In these studies, total ion current (TIC) chromatograms typically exhibit a large number of compounds with a broad dynamic range, and therefore may suffer from insufficient baseline separation of compounds.…”

“…This could potentially lead to peaks that are obscured by co-elutions and, therefore, are not detected, or potentially peak misidentification using mass spectrometry. Derivatization is often used to reduce matrix effects [2,5,9]; however, many TIC chromatograms in published literature still exhibit poor baseline separation likely due to co-elution with an unresolved complex mixture (UCM) coming from the matrix. Co-elution of peaks at the detector can result in poor mass spectral library matches, which may result in the lack of an identity assigned to a peak, or in a more unfortunate scenario, may cause peak misidentification.…”