| Abstract: |
Plant material and particularly non-wood products have played an important role for human cultures all over the world, as source of food but also of raw substances fulfilling material, spiritual, as well as medicinal requirements. Plant exudates and particularly dammar resins (Dipterocarpaceae family) were widely used in the past in Asia notably as waterproofing and caulking agents. Due to their prolonged burial since active use, these substances were partially or totally modified by alteration processes that profoundly affect their chemical composition and therefore their physical character, often resulting in misidentification arising from macroscopic observation. Molecular analysis of these complex organic remains provides clues to characterize the substances, to evaluate their degree of alteration, and to get some insight into their history in order to enhance our knowledge of technologies of past civilisations. This study focuses on the gas chromatography-mass spectrometry (GC-MS) characterisation of two organic samples, visually different in color and texture, collected in Khao Sam Kaeo during the 2006 excavation campaign: KSK06-P43-U4 (n°2307) and KSK06-P43-U4 (n°2308). These residues estimated to date from the 4th to the 2nd centuries BC, based on the dating of the geological strata where they were discovered, were suspected to be lumps of dammar because of their macroscopic aspect and their excavation context (East coast from Peninsular Thailand). To confirm these assumptions, the samples were analysed for biomarkers and their molecular profiles were compared to those of fresh dummars from various species collected in 2003 under the control of two palynologists in Lo Go Xa Mat, Vietnam. The analytical procedure applied to the analysis of these precious archaeological substances allows a detailed characterisation of their overall chemical composition by GC-MS, after fractionation enabling concentration of compounds, some of which are present in minute amounts. This procedure constitutes a powerful tool to identify biomarkers, allowing us to distinguish resins from different botanical sources, even very faded by alteration processes. The present study established that the two organic lumps excavated in Khao Sam Kaeo are made up of pure dammar from the Dipterocarpus genus. The two samples were collected via different tapping procedures: the use of thermal treatment to stimulate the resin flow has been evidenced for sample n°2307, whereas no definite conclusion could be drawn for sample n°2308. This latter sample could either correspond to the primary resin flow (that is to say flow stimulation) or stems from a secondary resin flow (after stimulation by another process than burning, for example after scrapping the incision), or could even have been collected in the ground near Dipterocarpaceae trunks. Molecular changes attributed to evaporation and leaching, as well as to radical photo-induced reactions have been detected in the two samples.
|
