The images are formed of conjugated, complex carbon-carbon double bonds within a carbohydrate layer of starch fractions and some saccharides. In many places this layer is clear. It is only in some places that complex carbon structures have formed; structures that absorb the right spectrums of the colors of light so they appear straw-yellow. Spectra analysis confirms this. Microchemical tests with iodine also detected the presence of starch impurities on the surfaces of linen fibers from the Shroud.
The impurity layer can be seen by phase-contrast microscopy. And with a scanning electron microscope the fine crystalline structure of the coating can be discerned. The image resists normal bleaching by chemicals or by sunlight, as is expected. But it can be reduced with diimide, also as expected.
The images are not paint, stain, dye or any form of pigment applied to the cloth by hand or mechanical means. They are a pattern of melanoidins, the same chemical products that give beer its color, toasted bread its brown, and bodies their tan from sunless tanning lotions.
The layer in which the color resides is as thin as the wall of a soap bubble. It is as thin in places as 180 nanometers and as thick in other places as 600 nanometers, and it coats only the extreme outermost fibers. By comparison, the average diameter of a linen fiber is 15,000 nanometers. The average human hair is 100,000 nanometers thick.
