What is the Diffusion Hypothesis of image formation?
An image formed by means of a Maillard reaction from a diffusion of amine vapors and a carbohydrate layer on the fibers of the Shroud is the leading image formation hypothesis. It is commonly referred to as the Diffusion Hypothesis.
The carbohydrate layer, or coating, consists of starch fractions and saccharides. It is thought that this layer formed when the cloth dried after being washed in suds of soapwort (Saponaria officinalis) to remove starch used during weaving.
The layers on the Shroud’s cloth are very thin. They have been observed using phase-contrast microscopy and the thickness has been estimated to vary between 180 to 800 nanometers. In places they have turned yellow and it is from this yellow color that the images are formed. Where they are imaged, that is to say yellow, they are chemically changed and thinner. This is consistent with a Maillard reaction. The cellular fibers, themselves, are not colored beneath the layer. This has been observed when the carbohydrate layer has been dissolved with diimide or peeled away with an adhesive. The layers are believed to be evaporation concentrations.
The Maillard reaction can take place naturally and the image color can be produced by amine gases produced by a dead body. They are very reactive. Within a few hours a body starts to produce heavier amines in its tissues such as putrescine (1,4-diaminobutane), and cadaverine (1,5-diaminopentane).
Raymond N. Rogers writes:
There is absolutely no doubt that the image color exists in a thin layer on the surface of image fibers. The layer is amorphous, and it seems to have an index of refraction relatively close to that of the linen fiber. The layer is quite brittle, and many flakes of the color have flaked off of the fibers. Colorless cellulose can be seen where image color has flaked off. The flakes can be seen and identified on the adhesive of sampling tapes. The flakes have the chemical properties of the intact image color on the fibers.