Middle Stone Age humans in East Africa may have employed complex techniques to process ochre for varied uses, such as body painting and creating stamps, according to scientists who found different types of processing tools in a 40,000-year-old cave.
Ochre fragments - which are rocks containing iron oxides, red or yellow in colour - have often been found at Middle Stone Age sites and have played a role in shaping the cultures of early African Homo sapiens.
Some researchers suggest that ochre was used for utilitarian purposes, for example in glue to adhere handles to tools, whilst others believe that the pigment was used for symbolic purposes, such as body painting or creating meaningful patterns.
However, few ochre processing tools have been studied in detail to understand how this material was processed.
Researchers including Daniela Rosso from the University of Bordeaux in France used microscopy, spectroscopy and X-ray techniques to analyse 21 ochre-processing tools and two ochre-stained artefacts from the Porc-Epic Cave, a 40,000-year-old Middle Stone Age site in Ethiopia.
The researchers found that the tools appeared to have been used to process different types of iron-rich rocks.
A range of stone types were used as grindstones, producing ochre powder of different colour and coarseness, likely employed to suit different functions, pointing to a high degree of behavioural complexity.
For example, finer powders would be most suitable for body painting, whereas coarser ochre would be suitable for functional uses.
One round stone appeared to have been painted or used as a stamp to apply pigment powder to different surfaces.
This is the first Paleolithic site to provide such comprehensive documentation of ochre processing techniques, researchers said.
"This study analyses the largest collection of such tools, found at Porc-Epic Cave, Dire Dawa, Ethiopia, in levels dated at c. 40,000 years ago," said Rosso.
"Ochre processing at Porc-Epic Cave reflects a high degree of behavioural complexity, and represents ochre use that was probably devoted to a variety of functions," he said.
The study was published in the journal PLOS ONE.