On the Late Breaking Website News page of shroud.com, Barrie Schwortz writes:
Recently, Joe Marino sent me a scan of a paper he and Sue Benford received from Ray Rogers on September 11, 2001. When I reviewed it I realized that, although parts of the paper had been included in several other papers by Ray, as well as in his book, A Chemist’s Perspective on the Shroud of Turin, nothing else Rogers wrote included all his observations and thoughts about image color in one dedicated article. So, with Joan Rogers’ participation, we proof read and reformatted the paper and replaced the images with higher quality versions, and are making it available here on Shroud.com in an article titled, An Alternate Hypothesis for the Image Color. Our thanks to Joe for bringing this to our attention. We hope you find it useful.
Here is why you must read the paper:
Without assuming anything other than an irregular nonmetallic surface and a cloth, heat would be transferred to the cloth by a combination of contact, convection, and radiation. Convection cells will vary in size and efficiency of heat transfer depending on clearance, and clearance will certainly vary with position. Contact points can supply energy that will flow radially from the point by conduction. The thermal diffusivity of cloth is quite low, but it is not zero. Given sufficient data, it should be possible to calculate temperature gradients across a cloth; however, the situation is much more complicated than a simple inverse square law.
With accurate chemical-kinetics values, it should be possible to calculate the temperature of a surface that would be sufficient to caramelize (color) any of the possible sugars or starches on a cloth and the amount of time required to reach any desired fraction of total decomposition.
I believe that a combination of relatively rapidly decomposing impurities on the surface of the cloth with transfer/diffusion of catalytic compounds from a body, as discussed by Pellicori, could explain the observations on the chemistry and appearance of the image on the Shroud. It should explain the shallow penetration of the image, the fact that the color did not penetrate more deeply at presumed contact points, its "half-tone" appearance, and its predominantly discontinuous distribution. Both catalyst concentration gradients and angle-dependent emittance of energy from a body would contribute to the 3-D relief seen in the image.
Pictured graph, taken from the paper, is from Gubareff, Torborg, and Janssen [Thermal Radiation Properties Survey, Honeywell Research Center, Minneapolis-Honeywell Regulator Co., Minneapolis, MN, 1960]. Ray sent me a copy years ago. It is worth taking the time to understand.