When they are exposed to air, copper surfaces become covered by a natural layer of cuprite (Cu2O).
Over time, this layer is slowly converted to other products of corrosion.
Until this century, relative dating was the only technique for identifying the age of a truly ancient object.
By examining the object's relation to layers of deposits in the area, and by comparing the object to others found at the site, archaeologists can estimate when the object arrived at the site.
Relative dating in archaeology presumes the age of an artefact in relation and by comparison, to other objects found in its vicinity.
Limits to relative dating are that it cannot provide an accurate year or a specific date of use.
Archaeology dating techniques can assure buyers that their item is not a fake by providing scientific reassurance of the artefact's likely age.
It compares various corrosion products that form over long periods of time and works with only a few nanograms of material so it causes almost no damage.
The dating process is always designed to try to extract the carbon from a sample which is most representative of the original organism.
In general it is always better to date a properly identified single entity (such as a cereal grain or an identified bone) rather than a mixture of unidentified organic remains.
Carbon-14, or radiocarbon, is a naturally occurring radioactive isotope that forms when cosmic rays in the upper atmosphere strike nitrogen molecules, which then oxidize to become carbon dioxide.
Green plants absorb the carbon dioxide, so the population of carbon-14 molecules is continually replenished until the plant dies.