birch pitch

Birch pitch (synonyms: birch bark pitch, birch tar) was the all-purpose adhesive of the Stone Age.

The earliest evidence comes from a middle Palaeolithic site at Koenigsaue in Saxony-Anhalt and has been dated to 80 000 years old. There is no evidence from the Upper Palaeolithic period. Birch pitch first reappears in the late Palaeolithic period (site at Kettig in the Central Rhine Valley). Evidence of birch pitch from the middle to the Late Neolithic period has been regularly found, both on the glued joints of a variety of artefacts and in raw lumps.

The first scientific investigations were carried out in the 19th century but it was the deployment of modern analysis methods beginning in the 1960's that provided sufficiently reliable insight into the composition of birch pitch and the conditions required for its manufacture. The investigations showed that birch pitch is a thermoplastic product which was extracted exclusively from birch bark by way of dry distillation, i.e. under the influence of heat and the exclusion of oxygen. It is liquid when hot and upon cooling becomes hard and, depending on the quality, brittle to tough. It is black in colour and gives off a characteristic smell when heated, the so-called Russia leather smell. In contrast to non-thermoplastic adhesives, birch pitch can be made soft and malleable again by careful heating. This property proved to be of great advantage when replacing damaged projectile points or blunted reaping knife components, for example.

The unfounded claim that Neolithic birch pitch was manufactured using ceramic vessels (known as retorts) has unfortunately persisted in archaeological literature to this day. The vessels which have been found partially filled with tar, and which are touted as apparent proof of this, must not have necessarily been used as "retorts". They may have merely been used for storing birch pitch. Furthermore, one would expect to find the remains of such retorts pretty regularly amongst the numerous preserved and exhaustively examined Neolithic ceramic inventories, which is not the case! It is, after all, indisputable that birch pitch was regularly manufactured in large quantities during Preceramic eras such as the Mesolithic period.

This means that modern scientific analysis was admittedly able to establish the precise basic conditions necessary for manufacturing birch pitch but that the Palaeolithic / Mesolithic / Neolithic method or methods of production are still unknown to this day! There are numerous finds of lumps of birch pitch from the Mesolithic and Neolithic periods which display dental impressions and which are often referred to as "chewing gum". However, the question of whether the material really was chewed for pleasure or merely to soften it remains unanswered.

©   Jürgen Weiner. Translation: Lois Ring
(Weiner,J. 1999: European Pre- and Protohistoric Tar and Pitch: A Contribution to the History of Research 1720-1999. Acta Archaeometrica 1, 1-109).

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