|Fuzzy dates from clay carbon dating|
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"Although the AMS dating of organic material in pottery once seemed a straightforward proposition, experience has shown it to be particularly challenging. There are several possible sources of carbon within the fabric of a pot, and occasionally as surface residues. Often the sherd is of low carbon, which means that a larger than usual amount of material is required for a direct date. The clay matrix might contribute old carbon, while the smoke and soot generated during ﬁring can be absorbed into the temper. If ﬁring uses old wood, results may be too early ... Hedges et al. (1992) have concluded that this technique is often unreliable due to theincorporation of carbon from the clay. Manning et al. (2011)have demonstrated in Mali that direct pot fabric radio carbon dates are 300–400 years older than OSL dates on the same sherd and at odds with dates of other more reliable organic remains. Kuzmin et al.(2001)have shown that a stepped combustion approach to dating pottery sometimes produces quite different ages with different temperatures, because temper-derived carbon tends tobe preferentially removed with a lower temperature combustion than the carbon bonded within the clay fraction."