Bark tar

D. Urem Kotsou, B. Stem, C. Heron, K. Kotsakis, Birch bark tar at Neolithic Makriyalos, Greece, Antiquity, 76, 962 967 (2002). 

S.N. Dudd, R.P. Evershed, Unusual triterpenoid fatty acyl ester components of archaeological birch bark tars, Tetrahedron Letters, 40, 359 362 (1999). 

Figures 3.4 3.6 report the average mass spectra obtained, respectively, for frankincense resin, mastic resin and birch bark tar [16]. Moreover, in each spectrum the main ion and ion radical fragments are assigned, and for each material the main molecular markers are shown.

Figure 3.6 Mass spectrum of birch bark tar obtained by DE MS...

The general pattern of the mass spectrum and the presence of peaks at mlz 424, 426 and 442, attributed, respectively, to the molecular ions of lupeol, lupenone and betulin, suggest the presence of birch bark tar. This study provided the first evidence that birch bark tar was used for assembling bronze tools during the Iron Age in Europe. 

Despite the complexity of the chemical composition of the resinous materials, in a few minutes such techniques provide a mass spectral fingerprint, which highlights the compounds that are the main components in the sample. They avoid any sampling treatment before analysis. They have thus enabled diterpenoid resinous materials from Coniferae, and several triterpenoid materials to be clearly identified. In particular, the DE-MS technique is able to distinguish between different triterpenoid materials such as mastic resin, frankincense resin and birch bark tar. In fact, using PCA on DE-MS mass... 

Figure 4.11 Mass spectrum of an archaeological sample made of a mixture of beeswax and birch bark tar from a residue sampled on a ceramic sherd from the Iron Age site of Grand Aunay (Sarthe, France). The spectrum was obtained by Dl El MS on a GCQ Finnigan device equipped with an ion trap analyser. Adapted from Regert and Rolando, 2002 (see colour Plate 1)...

Regert et al. studied [9] a series of 30 Neolithic hafting adhesives from lake dwellings at Chalain (France) using an analytical procedure based on GC/MS analysis involving solvent extraction (dichloromethane) and trimethylsilylation. In the majority of the samples a series of triterpenoid compounds with a lupane structure was clearly identified on the basis of their TMS mass spectra. In particular, the presence of betulin, betulone, lupenone, lupeol and lupa-2,20(29)-dien-28-ol allowed birch bark tar to be identified. In other samples the co-occurrence of other plant biomarkers such as a-amyrin,(3-amyrin... 

M. Regert, V. Alexandre, N. Thomas, A. Lattuati Derieux, Molecular characterisation of birch bark tar by headspace solid phase microextraction gas chromatography mass spec trometry a new way for identifying archaeological glues, J. Chromatogr., A, 1101, 245 253 (2006). 

Birch bark tar has been identified in numerous investigations of prehistoric samples, as residues of hafting on stone tools, as visible surface deposits on pottery vessels and as isolated finds, sometimes displaying clear evidence... 

The apparent deliberate selection and preparation of certain resources over others (birch bark tar over softwood products) is repeated throughout later European prehistory. Whilst we lack systematic comparative surveys of the physical properties of resin, heated wood and bark products, and bitumen, both choice and preference were being expressed. Yet, even if we had data of this nature, other factors are likely to have come into play. The ability to transform natural materials (such as wood or bark) into discrete organic substances then subject to myriad uses (hafting of tools and weapons just happens to be the most visibly persistent role) would have had a dramatic impact on those who made these substances. 

The Chemistry of Birch Bark and Birch Bark Tars... 

Hayek et al. (1990) reported the identification of 14 samples of birch bark tar of Chalcolithic to Early Iron Age date from sites in Austria and Denmark. In this study, authentic tars from bark samples of a number of different species (e.g., birch, oak, alder, hazel, elm and so on) were produced under laboratory conditions (using Kugelrohr distillation) and compared with the aged samples... 

The chemical composition of birch bark tar is dependent on the temperature at which tar is produced. In producing simulated tars in the laboratory for comparison with an adhesive used to repair a Roman jar from Stan wick, Charters et al. (1993) found that tars prepared at 350 °C displayed an increase in triterpenoid hydrocarbons as well as unresolved components presumably resulting from pyrolysis, although the precise nature of these molecules has not been elucidated. Binder et al. (1990) and Charters et al. (1993) also report the presence of allobetul-2-ene [Structure 7.24] in aged birch bark tars. Since this molecule has not been reported in extracts from fresh birch bark, it could be formed during heating to produce the tar (Regert et al., 2003). 

Research into samples of Mesolithic date, particularly those in Scandinavia, reveals the same preponderance of birch bark tar. Tar may not have only been used in hafting (Aveling and Heron, 1998) as some isolated lumps display clear evidence of human tooth impressions [see Aveling and Heron (1999), for consideration of the reasons]. Nine lumps of tar with human tooth impressions have been found at the Neolithic lake dwelling at Hornstaad-Hornle I, in southern Germany (Rottlander, 1981 Schlichtherle and Wahlster, 1986 92) and others are known from Mesolithic bog sites in Scandinavia (Larsson, 1983 75-76). It is plausible that birch bark tar served as a mild stimulant. A more prosaic interpretation is that chewing the tar rendered it more ductile for use. 

Aside from the characterization of birch bark tar, higher plant resins and their heated derivatives and beeswax, what potential remains for the identification of other organic substances used in prehistoric Europe This short summary intends to whet the appetite by briefly reviewing recent investigations and... 

Aveling, E.M. and Heron, C. (1998). The chemistry of birch bark tars at Mesolithic Star Carr. Ancient Biomolecules 2 69-80. 

Lucquin, A., March, R.J. and Cassen, S. (2007). Analysis of adhering organic residues of two coupes-a-socles from the Neolithic funerary site La Hougue Bie in Jersey evidences of birch bark tar utilisation. Journal of Archaeological Science 34 704-710. 

Stern, B., Clelland, S.J., Nordby, C.C. and Urem-Kotsou, D. (2006). Bulk stable light isotopic ratios in archaeological birch bark tars. Applied Geochemistry 21 1668-1673. 

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