This should be reported in the submission forms accompanying samples sent to the laboratory.Contamination may be artificially or naturally caused.Nevertheless, there are certain laboratory procedures which are associated with specific sample types and environments, and a number of accepted and often repeated pretreatment methods. The laboratory decides on the most effective pretreatment procedure through a careful examination of each submitted sample.A number of variables feature in this consideration, one of the most important concerns the environment within which the sample was deposited.When the C14 method was originally developed, Libby and his research team had to assume that the ratios of the carbon isotopes they were measuring had been altered only by 14C decay (Taylor, 1987:3) and that the sample material accurately represented the event to be dated.Sample materials deposited in archaeological or geological contexts seldom remain in pristine condition, of course, they are often degraded and altered chemically.A stratigraphical diagram should be drawn to enable the dater to understand completely the site and origin of the material, and to consider the ability of the lab to adequately date the sample in question.The submitter should also indicate the degree of accuracy and precision required.
This surface exchange is termed 'adsorption' and is especially common in samples such as peats, charcoals and muds.
The following types of sample have been commonly radiocarbon dated: Since the 1950's, a number of researchers have concentrated on investigating and reducing the effects of this post-depositional contamination.
This field of inquiry is known as sample pretreatment and it is concerned with removing post-depositional contaminants by isolating sample fractions containing carbon which is autochthonous and therefore accurately dates the event in question.
Sometimes, a precise date is not needed and pretreatment methods designed to reduce errors will not be necessary.
Many commercial laboratories have different charges for dating depending on the precision (and speed) that is required.