Birch tar is the oldest manmade adhesive dating back to the European Middle Palaeolithic. Its study is of importance for understanding the cognitive capacities and technical skills of Neanderthals and the aceramic production systems employed in the European Palaeolithic and Mesolithic. Several methods may have been used to make birch tar, the most common proposition being dry distillation in oxygen-depleted atmospheres. One of the major impediments for our understanding of the conditions employed to make Neanderthal birch tar, and ultimately the technique used, is that it remains unknown at which temperatures exactly birch tar forms. The relationship between heating duration and tar formation is also unknown. To address these questions, we conduct a laboratory heating experiment, using sealed glass tubes and an electric furnace. We found that birch tar is only produced at a narrow temperature interval (350 °C and 400 °C). Heating times longer than 15 min have no effect on the quantity of tar produced. These findings, notwithstanding previous propositions of necessarily long heating times and larger tolerances for temperature, have important implications for our understanding of the investment in time needed for Palaeolithic birch tar making.

桦木焦油是最早可追溯至欧洲旧石器时代的人造胶。它的研究对于了解尼安德特人的认知能力和技术技能以及欧洲旧石器时代和中石器时代的陶瓷生产系统具有重要意义。可能已经使用了几种方法来制备桦木焦油，最常见的建议是在贫氧气氛中进行干馏。对我们了解制造尼安德特人桦木焦油的条件以及最终使用的技术的主要障碍之一是，尚不清楚在什么温度下确切形成桦木焦油。加热时间和焦油形成之间的关系也是未知的。为了解决这些问题，我们使用密封的玻璃管和电炉进行了实验室加热实验。我们发现桦木焦油仅在狭窄的温度区间（350°C和400°C）下产生。加热时间超过15分钟不会影响焦油的产生量。尽管先前提出的建议是必须较长的加热时间和较大的温度公差，但这些发现对我们理解旧石器时代的桦木焦油生产所需的时间投资具有重要的意义。