Material intrusion contamination is well known problem in carbon 14 dating. A classic example is peat bogs. Very old bogs often contain miniscule roots from newer plants that grew in the peat. The roots of these plants, sometimes having decomposed, are nearly indistinguishable from the decomposed material of older peat. What ends up being carbon dated is a mixture of old and new material which produces an average, meaningless C14 age.
No one seemed to consider, in 1988, that material intrusion might be a serious problem with the Shroud of Turin carbon dating even though several clues existed.
In the case of the Shroud, it was a material intrusion of mending threads that were dyed to look older and match threads in the cloth. It wasnt the threads of the Shroud itself that were dyed. It was a small area in one corner of the Shroud where some mending had taken place. Chemical analysis clearly shows this even though it is hard to detect visually.
It was from the mended area that carbon 14 samples had been cut in 1988.
