Palaeolithic painting matter: natural or heat-treated pigment?

Analyses of archaeological materials attempt to rediscover the know-how of Prehistoric men by determining the nature of the matter, its preparation mode, and its geographic origin. The preparation mode of painting matter of Palaeolithic rock art consisted not only in mixing and grinding but also in heat-treatment. Palaeolithic painters used two main colors: red (iron oxide, hematite) and black (charcoal or manganese oxide). The different phases of manganese oxides can be distinguished using their elemental composition, their structure and the oxidation state of the Mn ion (II, III, IV). Their transformation during heat-treatment has been studied on mineralogical reference samples by means of transmission electron microscopy (TEM) either coupled or not with a heating stage (in situ). These studies have enabled us to understand the transformation mechanisms of manganese oxides and also to gain insights into the preparation procedures of painting materials during the Palaeolithic period. The painting samples studied in this paper come from the cave of Lascaux (Dordogne, France). These studies allow us to distinguish between natural or heat-treated manganese oxides.