They placed a linen sheet flat over a volunteer and then rubbed it with a pigment containing traces of acid. A mask was used for the face.
The pigment was then artificially aged by heating the cloth in an oven and washing it, a process which removed it from the surface but left a fuzzy, half-tone image similar to that on the Shroud. He believes the pigment on the original Shroud faded naturally over the centuries.
They then added blood stains, burn holes, scorches and water stains to achieve the final effect.