Birch bark tar and jewellery: The case study of a necklace from the Iron Age (Eckwersheim, NE France)

Abstract

Organic residue analysis has been undertaken on an organic material found on a necklace with a pendant unearthed from a necropolis dated to the Early Iron Age (800-475 BC) and located in Eckwersheim (NE France). The molecular composition of the substance, which was investigated using gas chromatography coupled to mass spectrometry, points towards an adhesive used to stick two bronze half-spheres to form a pendant. The predominance of triterpenoids from the lupane series led to the identification of the adhesive as a birch bark tar and constitutes a rare example of the use of such a material in jewellery in the past.

Betulin-related esters from birch bark tar: Identification, origin and archaeological significance

“…The triterpenoids notably comprised betulin T1, lupeol T2 and betulone T3 which are native triterpenoids occurring in birch bark (Hayek et al, 1989(Hayek et al, , 1990Schnell et al, 2014). However, these compounds represent generally by far the predominant triterpenoids in the case of fresh (or even weathered) birch bark (Hayek et al, 1990;Aveling and Heron, 1998;Schnell et al, 2014;Courel et al, 2018), whereas they appear only as minor constituents in the archaeological sample. In the latter case, the distribution is dominated by compounds T4, T5, T10, T7 and T11, which all belong to the series of D 2 -betulin-related triterpenoids.…”

“…In the latter case, the distribution is dominated by compounds T4, T5, T10, T7 and T11, which all belong to the series of D 2 -betulin-related triterpenoids. These compounds, together with the allobetulane derivatives T10-T13, are known from the literature to be Version avant révision biomarkers of birch bark tar (Bosquet et al, 2001;Modugno et al, 2006;Regert et al, 2006;Courel et al, 2018;Rageot et al, 2019).…”

“…Δ 2 -triterpenoids are formed by elimination of the oxygenated function at C-3 of lupeol T2 and betulin T1, this reaction being generally induced by a thermal treatment as is the case for the preparation of birch bark tar (Courel et al, 2018;Rageot et al, 2019). Similarly, it was shown that the same thermal treatment leads to the formation of allobetulane derivatives (T10-T13) which results from an acid-catalyzed intramolecular rearrangement of the ring E of betulin and by-products (Davy et al, 1951a(Davy et al, , 1951bGreen et al, 2007;Salvador et al, 2009).…”

“…Among them, birch bark tar is a vegetal substance produced by dry distillation of birch bark (Aveling and Heron, 1998;Urem-Kotsou et al, 2002;Rageot et al, 2016;Courel et al, 2018). This sticky and hydrophobic material has been used since the Paleolithic (Koller et al, 2001;Grünberg, 2002) for various purposes, like the hafting of lithic tools or jewellery (Sauter et al, 2000;Bosquet et al, 2001;Koller et al, 2001;Courel et al, 2018), the repairing or caulking of ceramics (Charters et al, 1993;Connan et al, 2000;Bosquet et al, 2001;Rageot et al, 2016;Reunanen et al, 1993;Urem-Kotsou et al, 2002), the decorating of ceramic vessels (Vogt, 1949) and has even been used as chewing-gum (Aveling and Heron, 1999;Karg et al, 2014). Birch bark tar has a typical molecular composition, making it easy to identify by detection of predominant lupane-related triterpenoids using gas chromatography coupled to mass spectrometry -GC-MS - (Hayek et al, 1989(Hayek et al, , 1990Reunanen et al, 1996;Aveling and Heron, 1998;Schnell et al, 2014).…”

Triterpenoids from Balsams: Useful Markers to Recognize Genuine, Adulterated and Archaeological Resins

“…pereirae) has thus been carried out using gas chromatography-mass spectrometry (GC-MS) to explore, in particular, the potential of triterpenoids as chemotaxonomic indicators. Triterpenoids, which could indeed be successfully used for the characterisation of various resinous archaeological materials (other than balsams) comprising frankincense (e.g., Brettell et al, 2015), Pistacia resin (e.g., Stern et al, 2003) and birch bark tar (e.g., Courel et al, 2018), can be considered as more reliable markers than benzoates/cinnamates. Up to now, only few studies were dedicated to the triterpene composition of balsams (e.g., Hovaneissian et al, 2008).…”