It is also standard to coat fossils during their extraction and transport.
Egyptologist speculate that that this might be so for some mummies, but not so for others.
It is produced in the upper atmosphere by radiation from the sun.
(Specifically, neutrons hit nitrogen-14 atoms and transmute them to carbon.) Land plants, such as trees, get their carbon from carbon dioxide in the air. The same is true of any creature that gets its carbon by eating such plants. Suppose such a creature dies, and the body is preserved.
It is important, as well, to obtain multiple samples at different places on an object and then use statistical methods determine a reasonable range of ages.
Yet, even with ideal conditions, carbon-dating results can be highly erroneous or unexpected.
A bar of pure uranium, for instance, would consist entirely of atoms with atomic number 92.