Nearly 20 years ago the Catholic Church invited me to determine chemically what the image is on the Shroud of Turin.

I obtained 32 samples from the shroud: 18 from areas where there are images both of a body and of bloodstains) and 14 from non-image areas (some from clear areas that served as controls, others from scorch and water stains caused by a fire in 1532). The samples were taken with squares of sticky tape, each of which exceeded a square inch in area and held more than 1,000 linen fibers and any materials attached to the shroud. They were excellent samples. I used standard forensic tests to check for blood. I found none. There is no blood on the shroud.

To determine what substances are present in the shroud images, I conducted tests based on polarized light microscopy. I identified the substance of the body-and-blood images as the paint pigment red ochre, in a collagen tempera medium. The blood image areas consist of another pigment, ver-milion, in addition to red ochre and tempera. These paints were in common use during the Middle Ages.

The paint on the shroud was dilute (0.01 percent in a 0.01 percent gelatin solution). I made up such a paint and an artist friend, Walter Sanford, painted an excellent shroud-like image (see photo at right and my book Judgement Day for the Shroud [Chicago: Mccrone Research Institute, 1996]. pp.145.149). Known as grisaille, the style of the painting, with its very faint, monochromatic image, was also common in the 14th century.

Based on the complete absence of any reference to the shroud before 1356, Bishop Henri of Poitiers's statement that he knew' the artist, the 14th-century painting style and my test results, I concluded in two papers published in 1980 that the shroud was painted in 1355 ('to give the paint a year to dry"). A third paper in 1981 confirmed these results with X-ray diffraction, scanning electron microscopy and energy dispersive X-ray determination of the elements present (iron, mercury and sulfur) in the two paints. Eight years after my published results, the carbon-dating results were reported as 1325 ± 65 year - thus confirming my date of 1355.