A piece of charcoal may be quite old before being picked up to construct a drawing. The main disadvantage of this is that such “beeswax” rock art is very rare, as far as I know occurring only in one area in Australia.A documented example of that occurred at a site in Australia. Inorganic pigments were far more frequently used than charcoal or other organic pigments in making rock paintings.Signals of this kind are often used by chemists studying natural environments.A hydrocarbon found in beach sediments, for example, might derive from an oil spill or from waxes produced by plants.This situation occurs when wood that has been dead for a long time, but has simply not decayed yet, is burned forming charcoal.It also occurs when the central portions of a very old tree are burned, again yielding charcoal. The radiocarbon date indicated that the charcoal graffiti was about 1300 years old!Isotopes participate in the same chemical reactions but often at differing rates.When isotopes are to be designated specifically, the chemical symbol is expanded to identify the mass (for example, C is not stable.
The third major dating technique utilizes plasma-chemistry to extract any organic material that is present in the mineral-pigmented paints. The first is when no organic matter was added initially to produce the paint.A second potential problem, particularly important for dating of charcoal paintings, is the so-called “old charcoal” problem. This is a problem that is present in all dating of charcoal paintings, and one that is generally undetectable.This situation occurs when the rock artist uses a piece of charcoal that just happens to have been lying on the ground for an undetermined length of time. In the second category of rock art dating, organic pigments or organic inclusions, the problems are perhaps less difficult than for other techniques. Dating of organic “beeswax” paintings in Australia is the only situation to my knowledge where replicate samples of a particular painting were dated by two different research groups, 80 years ago, was not great (10 %).The first radiocarbon dates on rock paintings were in 1987 on charcoal pigments, in some ways the most straight forward method.Dating charcoal is the best tested technique as it has been used extensively since the beginning of radiocarbon dating.This reduction in sample size opened the way for even the small amounts of organic matter in rock paintings to be dated starting a decade later in 1987.