A sample with a real age of 40000 years, only containing 1% of recent carbon, would yield an apparent age of 32800 years, which corresponds to a rejuvenation of 7200 years!
(figure 1Therefore the main cause of error in radiocarbon dating is the presence of recent carbon leading to more recent dates.
In order to date red paintings and engravings, indirect methods allow us to estimate the age of the deposits that form after the completion of the art works.
These techniques are thermoluminescence (TL) and the uranium/thorium series, applicable to calcite deposits in caves, the dating of calcium oxalate coating and amorphous silica patinas that form on rocks exposed to daylight and lastly, optically stimulated luminescence (OSL), a technique used to date the sediments related to parietal art.
In this article on absolute dating methods, we will briefly recall the scientific principles on which the different methods are based, in order to allot more scope to the causes of error that blur our overall vision, but also to recent technological progress which offers an optimistic outlook for the future of our discipline.
Most of this paper will deal with carbon-14 as it is the only direct dating method applicable to parietal art (although it is limited to charcoal drawings).
An ultrafiltration technique isolates collagen macromolecules, which often results in much older dates (Higham , 2006; table 2).
The technique consists in subjecting the sample to additional known irradiation doses, in order to calculate the paleodose (which is to say the irradiation that the sample was exposed to during the period of time since it was last heated (for flint), or since its formation (for calcite).
Calcium oxalate deposits can be mixed in with pigments and skew the results as their age can vary from the age of the paintings to the present-day (see below the paragraph on oxalates).