Alizarin was a common medieval dye produced from madder root. The carbon 14 sample area of the shroud contains alizarin dye; something that is not found elsewhere on the full cloth.
Some of the alizarin dye was complexed with a common mordant, alum (hydrous aluminum oxide). The carbon 14 samples also contain cotton fibers and spliced threads where apparently newer thread was dyed to match age-yellowed older thread.
In addition to alizarin, other dyestuffs, cotton fibers and spliced threads are also not found elsewhere on the Shroud. As chemist Raymond Rogers wrote in the peer-reviewed, scientific journal Thermochimica Acta, "The combined evidence from chemical kinetics, analytical chemistry, cotton content, and pyrolysis/ms proves that the material from the radiocarbon area of the shroud is significantly different from that of the main cloth. The radiocarbon sample was thus not part of the original cloth and is invalid for determining the age of the shroud."
Thus the sample used suffered from what carbon 14 scientists call material intrusion.
