Famed microanalyst, Walter C. McCrone, examined 32 tape-lifted samples from the Shroud of Turin and identified the 'blood' as tempera paint containing red ochre and vermilion along with traces of rose madder, pigments used by medieval artists to depict blood. McCrone was held to a secrecy agreement. A Swiss criminologist, Max Frei-Sulzer, said that McCrone had found certain pollen grains on the cloth that "could only have originated from plants that grew exclusively in Palestine at the time of Christ," a claim that McCrone denied.
Frei-Sulzer reported finding numerous types of pollen from Palestine on tape-lifted samples from the Shroud, but other tape-lifted samples taken at the same time showed few pollen. Micropaleontologist Steven D. Schafersman was probably the first to publicly suggest Frei-Sulzer may be guilty of deception.
When Frei's tape samples became available after his death, McCrone was asked to authenticate them. He authenticated the actual tapes because "it was easy to find red ocher on linen fibers much the same as I had seen them on my samples." But there were few pollen other than on a single tape which bore 'dozens' in one small area, consistent with the tape having been subsequently 'contaminated', McCrone concluded, by having been pulled back and the pollen surreptitiously introduced.