A scientific theory that does not rule out the association of the shroud with Jesus involves the gases that escape from a dead body in the early phases of decomposition. The cellulose fibers making up the shroud's cloth are coated with a thin carbohydrate layer of starch fractions, various sugars and other impurities. This layer is very thin (180 - 600 nm) and was discovered by applying phase contrast microscopy. It is thinnest where the image is and appears to carry the color, while the underlying cloth is uncolored. This carbohydrate layer would itself be essentially colorless but in some places has undergone a chemical change producing a straw yellow color. The reaction involved is similar to that which takes place when sugar is heated to produce caramel.
In a paper entitled "The Shroud of Turin: an amino-carbonyl reaction (Maillard reaction) may explain the image formation," (see References) R. N. Rogers and A. Arnoldi propose this natural explanation (which does not rule out a supernatural invocation or enhancement of a natural process). Amines from a human body will have Maillard reactions with the carbohydrate layer within a reasonable time, before liquid decomposition products stain or damage the cloth. The gases produced by a dead body are extremely reactive chemically and within a few hours, in an environment such as a tomb, a body starts to produce heavier amines in its tissues such as putrescine and cadaverine. These will produce the color seen in the carbohydrate layer. But it raises questions about why the images (both ventral and dorsal views) are so photorealistic and why they were not destroyed by later decomposition products (a question obviated if the Resurrection occurred, or if a body was removed from the cloth within the required timeframe).
