Abstract
Abstract:
The production of compound adhesives using disparate ingredients is seen as some of the
best evidence of advanced cognition outside of the use of symbolism. Previous field and
laboratory testing of adhesives has shown the complexities involved in creating an effective
Middle Stone Age glue using Acacia gum. However, it is currently unclear how efficient different
adhesive recipes are, how much specific ingredients influence their performance,
and how difficult it may have been for those ingredients to be combined to maximum effect.
We conducted a series of laboratory-based lap shear and impact tests, following modern
adhesion testing standards, to determine the efficacy of compound adhesives, with particular
regard to the ingredient ratios. We tested rosin (colophony) and gum adhesives, containing
additives of beeswax and ochre in varying ratios. During both lap shear and impact tests
compound rosin adhesives performed better than single component rosin adhesives, and
pure acacia gum was the strongest. The large difference in performance between each
base adhesive and the significant changes in performance that occur due to relatively small
changes in ingredient ratios lend further support to the notion that high levels of skill and
knowledge were required to consistently produce the most effective adhesives.