Background radiocarbon activity is measured, and the values obtained are deducted from the sample’s radiocarbon dating results.
Background samples analyzed are usually geological in origin of infinite age such as coal, lignite, and limestone.
A radiocarbon measurement is termed a conventional radiocarbon age (CRA).
The CRA conventions include (a) usage of the Libby half-life, (b) usage of Oxalic Acid I or II or any appropriate secondary standard as the modern radiocarbon standard, (c) correction for sample isotopic fractionation to a normalized or base value of -25.0 per mille relative to the ratio of carbon 12/carbon 13 in the carbonate standard VPDB – Cretaceous belemnite formation at Peedee in South Carolina, (d) zero BP (Before Present) is defined as AD 1950, and (e) the assumption that global radiocarbon levels are constant.
An age could be estimated by measuring the amount of carbon-14 present in the sample and comparing this against an internationally used reference standard.
It must be noted though that radiocarbon dating results indicate when the organism was alive but not when a material from that organism was used.Standard errors are also reported in a radiocarbon dating result, hence the “±” values.