The use of ochre 40,000 years
ago in Africa
In the case study presented here, the aim of our research was to achive a
better understanding of ochre use by Middle Stone Age populations in East
Africa through the analysis of 4,213 pieces of iron-rich mineral fragments(40 kg) found at the archaeological site of Porc-Epic Cave, Ethiopia, in layers
dated to ca. 40,000 years ago (Rosso, d’Errico and Queffelec 2017).
The term “ochre” refers to a variety of rocks characterized by a red or yellow
colour or streak, from soil lumps to ore minerals, containing a high proportionof iron oxides. A large number of ochre pieces discovered at this site show
traces of utilization, in particular flaking scars and striations produced bygrinding. Twenty-one grindstones used for ochre processing were also
recovered at the site (Rosso, Pitarch Martí and d’Errico 2016) in the same
areas where most of the ochre pieces were found (Rosso, d’Errico and Zilhão2014). The purpose of the tribological analysis, conducted in tandem withmore classical analytical techniques, was to better understand how ochre
pieces were processed and used.
The analyzed samples included ochre pieces bearing facets createdby grinding (figure 1). Even though these facets are often described inliterature, there have been no attempts to characterize them quantitatively.
Experimental grinding of ochre lumps similar to those found at the site on
grindstones made of different rocks allowed us to create a comparative
framework. We recorded the variables commonly used to characterizefacets (size, presence of grooves or striations, localization on the fragmentetc.) and conducted a non-destructive tribological analysis by using a 3D
optical profiler.
CASE STUDY THE USE OF OCHRE 40,000 YEARS AGO IN AFRICA

This paper is authored byAlain Queffelec, Daniela Rossoand Francesco d’Errico. Theseresearchers belong to the PACEA
laboratory, a research unit of theCentre National de la Recherche
Scientifique (CNRS), the Universityof Bordeaux, and the French
Ministry of Culture. PACEA researchmostly focuses on Palaeolithic
cultures in Europe and Africa andtheir environment, biologicalanthropology, funerary practices,and rock art.

1Figure [1] Ochrefragments modifiedby grinding(top left) and byscraping (bottomleft) with close-up
views illustrating
traces diagnosticof the techniqueused (modified after
Rosso et al. 2017).

■ Measurements
The study was conducted on nineteen archaeological pieces of fine-grainedochre presenting one or more facets, and three very fine-grained, finegrained and coarse-grained experimental ochre pieces. Each of them wasabraded on limestone, quartzite and sandstone grindstones.
In order to capture large areas, we measured an area of 5x5 fields of view
obtained with the 20X brightfield objective of Sensofar’s S neox witha Z-range of few millimetres. Some of the resulting surfaces, after dataprocessing (form and outlier removal, filling of non-measured points) are
shown in figure 2.

Figure [2] 3D renderings of experimental (A, B, C) and archaeological (D to L) facets measured

using confocal technique (modified after Rosso et al. 2017).

Gaussian filtering (0.25 mm cut-off ) was applied to focus only on roughness
and, after testing multiple standard parameters (ISO 25178), Sq and Sdr
appeared as the most effective choice to discriminate experimental facets(figure 3A). In some cases results highlight significant differences in theroughness values recorded on facets belonging to the same ochre piece.
2CASE STUDY THE USE OF OCHRE 40,000 YEARS AGO IN AFRICA

This suggests that some ochre fragments were processed on different
grindstones, arguably at different times, to produce small quantities of ochre
powder. Colorimetric and granulometric analyses, conducted in parallel,
indicate that the resulting powders differed in colour and grain size andwere used for different purposes, either functional or symbolic in nature(Rosso, d’Errico and Queffelec 2017).

Figure [3] Scatter plots correlating Sq and Sdr values on experimental and archaeologicalfacets. (a) results obtained when grinding very fine-grained ochre (EXP1), fine-grained ochre(EXP2) and coarse-grained ochre (EXP3) on grindstone made of different rocks. (b) Results ofthe roughness analysis of ground facets on archaeological pieces. Dots of the same colour
identify measurements taken on the same facet. Grey dots identify the overall variability of thearchaeological sample (modified after Rosso et al. 2017).

■ Conclusions
Confocal technology is an effective technique to identify facets of ochre
pieces ground on different rocks. Results were instrumental to improving
our understanding of ochre processing and use by the Middle Stone Agehominins that inhabited Porc-Epic Cave 40,000 years ago. Application of thesame methodology to collections of ochre pieces from other Middle Stone
Age sites may identify changes through time in the way ochre was modified,provide key information on the function it fulfilled in those societies, andhelp establish when pigments were first used symbolically in the history ofmankind.

CASE STUDY THE USE OF OCHRE 40,000 YEARS AGO IN AFRICA

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