Carbon dating fabric
For practical reasons, which are discussed later, the value of "modern" is defined by reference to two primary standards of known radiocarbon content.These two standards were measured by many different laboratories to determine the value of the standards relative to "modern." Because the production rate of C is not a constant, we need to make corrections for this effect, as discussed in the following sections.Large sample sizes were needed for both counting methods, which limited their usefulness in such applications as studies of artwork, where only small samples could be taken.
Accelerator mass spectrometry (AMS) is a technique for direct measurement of the concentration of radioisotopes.
Because plants absorb carbon from the atmosphere during photosynthesis, and as animals eat plants, the animals will also contain the same level of C in a sample with that in "modern" material, defined as 1950 AD.
We can equally well use a different standard if we know its relation to "modern," or 1950 AD.
To obtain a truly absolute chronology, corrections must be made, provided by measurements on samples of know age.
The most suitable types of sample for radiocarbon dating are charcoal and well-preserved wood, although leather, cloth, paper, peat, shell and bone can also be used.