For my position, I do not discount McCrone finding iron oxide and vermilion particles on the shroud. The question is – is it sufficient to account for all of the body image and the blood stains? Again, even McCrone admits he cannot demonstrate this scientifically:
I am not saying the Shroud is not authentic. I am saying that the image area has a lot of iron
oxide and a lot of artist’s pigment associated with it but I do not know whether the amount of
iron oxide present is sufficient to explain the entire image.
In his paper, he admits only a small amount was visually detected:
There are very small amounts of pigment and me-
dium on the body-image fibers, undetectable except by
careful light microscopy at a minimum magnification
of 400x. The blood-image areas hold more solid ma-
terial as red ochre, vermilion, and collagen tempera but,
still, much less than a normal painting.
So, what explains the presence of trace amounts of iron oxide and vermillion? He acknowledges the explanations by STURP:
authors admit that the Shroud has protein, Fe2O3, and
HgS in image areas, but attribute the protein to blood,
the iron oxide to retting of the flax to form linen fibers,
and the vermilion to contact of the Shroud with painted
replicas (to transfer the divine powers of the Shroud).
It should be noted he provides no counter to these explanations and does not dispute them.
Alan Adler comments on particles found on the TS:
There is a relatively large amount of extraneous debris found on the surface of the Shroud,(5,7) e.g., wax, red silk fibers from the backing cloth, occasional traces of various types of artist’s pigments (ascribed to either the artist who painted the Shroud itself(5) or alternatively to artists making copies of the Shroud and then sanctifying the copy by contacting it to the origina(l7)), pollens, hairs, insect parts, etc. Some of this material has historic value and context.
So, by examining sticky tape samples, one could find a multitude of different kinds of particles, but that does not mean the entire shroud would be imaged by any of those particles.