Dating Ancient Art

Scientific methods of dating ancient art have been developed only relatively recently. Without dates, a theoretical evolutionary model lacking any scientific foundation was long used, and it is still occasionally applied. Its basis is that the older an artwork is, the cruder it must be, which supposes a belief in the linear development of artistic creation, with constant progress made over centuries and millennia. Each time it has been possible to establish solid chronologies, however, this model has proved false. Such was the case for the wall art of Paleolithic (from 3.3 million years ago until 9650 B.C.E.) European caves, when the discovery of the Chauvet cave revealed that from extremely ancient times the visual appeal of the art was extraordinary.

Radiocarbon dating is one method for dating ancient artworks. It is based on the fact that all living organisms contain a very small amount of radioactive carbon identical to that contained in the atmosphere. After death, the organism ceases interacting with the air, and the radioactive carbon gradually disintegrates. We know that it loses half its mass in 5,568 years. Residual microradioactivity can be measured to calculate the date of the organism's death. A sufficient quantity of organic (carbon-containing) matter is indispensable for applying this method. This means that radiocarbon dating is not currently possible for engravings or sculptures, or for paintings made with mineral pigments (coloring substances), but only for those in which carbon was used, or those whose binding agent—the material used to give cohesion to the paint—is organic (blood, plant gum, or fat, for example) or contains an adequate amount of organic matter.

Therefore, because the vast majority of rock art cannot be dated directly, we try to date it indirectly by establishing either a maximum or a minimum possible age.At times, geologic phenomena provide a solid point of reference. For example, we know that in Scandinavia the sea was 80 meters higher before the Neolithic, 8,000 years ago, than it is today.So if we find carvings at an altitude of 40 meters, they clearly can only belong to a later period, such as the Bronze Age (3200-600 B.C.E.).On the Big Island of Hawaii, with its very active volcano, lava dating back just 600 years has been engraved: these engravings obviously are less than six centuries old.

In other cases, we can evaluate a work's age by assessing its current state or by considering its immediate environment. In the dryness of deserts, rock engravings change appearance as their patination—a thin outer layer that develops over time—darkens. Consequently, whether in Niger or in New Mexico, the lightest carvings obviously are the most recent. This method, however, gives only a relative indication of age. In the United States and Australia, among other places, attempts have been made to obtain more definitive indications by radiocarbon dating old patination from the organic elements it has trapped. These methods are still experimental and controversial, for in fact it is not clear what is being dated, as the constituent elements of the outer layer may have been integrated into it at various times and may therefore be of different ages.

It is also possible to establish minimal dates when paintings or engravings are partially covered by deposits that can be more faithfully dated than the patinations. In parts of Australia, wasp nests that have formed on drawings can, when they are very old, provide valid and useful dates. In other instances, dating fragments of decorated walls that have broken away, fallen, and been covered up by archaeological layers will give a minimal age, as is the case with the Early Man shelter and Carpenter's Gap in Australia and a western Cape shelter in South Africa. This archaeological approach proves even more precise when tools, paints, and other materials used to create the drawings are discovered in a well-dated layer nearby: we then know that the date of the layer will be the date of the paintings. Such was the case with the Bidon cave in France, where splotches of red paint identical to that used in some of the paintings were discovered at the foot of the painted wall. Because the layer in which these splotches were found included coal (organic material), the layer could be radiocarbon-dated to about 21,650 years ago.