Approaches to dating rock paintings
The processes and materials used and the antiquity of rock paintings have always been of interest to archaeologists (e.g. Watson 1967; 1969). However, until recently few methods were available to provide answers to questions about the antiquity of rock pictures. Questions concerning temporal social interactions and relationships, cultural developments and interchanges between different linguistic groups have been based primarily on painting styles and relative chronologies (e.g. Chaloupka 1984; Lewis 1988; David & Cole 1990; David et al. 1990).
Prehistoric paints are difficult materials to date because they are generally composed of naturally occurring and geologically old ochres, clays and other pigments. The range of inorganic pigments, ochres, fillers and organic dyes available to prehistoric artists was immense (Leechman 1937; Watson 1967; Rudner 1982; Zolensky 1982: Clottes et al. 1990; Watchman 1990c). Iron oxides and aluminium silicates, the essential ingredients of ochres and clays, do not contain any known materials which can currently be used to date a painting.
In recent times rock art chronologists have tried to adapt easel painting authentication strategies to the absolute dating of rock paintings. However, some of these approaches are unsuitable for dating prehistoric rock paintings. For instance, dating the rock beneath paintings will yield an age for the igneous, metamorphic or sedimentary rock-forming process and not the time of painting.
Chaloupka (1984) attempted to establish a chronology for some northern Australian rock art by making correlations between changes in palaeoenvironmental conditions and superimpositions of depictions of fauna and flora in rock painting motifs. General limiting ages can also be assigned to paintings of extinct animals (Brandl 1972; Wright 1972; Lewis 1977). Rock paintings of horses, ships, aeroplanes and men with guns in Australia, Africa and North America are obviously relatively recent. Almost all other motifs have not yet been dated absolutely, but this situation is changing.
A major problem facing rock painting chronologists is that indigenous people around the world regard rock painting sites as sacred or highly significant places. Sampling must therefore be done with extreme care and respect, not only for the artefact but also for the people whose heritage is being studied. Damage to paintings must be minimized and so technological and innovative approaches are necessary.
The AMS 14C dating method is generally accepted by archaeologists, geomorphologists and geologists as a reliable way of dating organic matter. Current research into the absolute dating of rock paintings is aiming either to date organic matter which was deliberately or accidentally incorporated in paints during paint preparation, or to determine the ages for layers containing organic substances under and over paintings. When interpreting dating results, consideration must always be given to the source of the original sample. The question 'What precisely was dated?' should always be asked.
Dating organic binding media in paints
Evidence for the presence of organic substances in paints is found throughout the ethnological literature, though most of it is highly speculative. In North America, for example (Grant 1967: 13)
For rock painting the pigment was reground and mixed with some sort of oil binder to give it permanence. The type of binder certainly varied from place to place, but animal oils, blood, white of egg, and vegetable oils were all readily available and would serve the purpose.
Dewdney & Kidd (1967: 169) mentioned the use of spittle mixed with pigment and also stated that 'beaver tails and fish roe, the hoofs of moose and deer, could all be used to make glue, and fish and rabbit skins may have been utilised also'.
The Luiseno of California ground parched kernels of chilicothe (Echinocystis macrocarpa) with hematite (Harrington 1933: 142). …