Understanding the nature of the Shroud of Turin's images

We need to begin by explaining briefly how the cloth was made; for in understanding that, we can understand how the images are formed.

1) Fibers, much thinner than human hair, were handspun together to form the yarn used to weave the linen cloth.

2) Individual lengths (hanks) of the yarn were bleached with potash. This is not an exacting method and thus some hanks of yarn were whiter than others.

How do we know this? The variation in bleaching caused a horizontal and vertical variegated appearance in the cloth; a faint plaid forming as different hanks of yarn were fed into the loom. As the cloth aged and naturally yellowed, the variegation became more pronounced as can be seen in the contrast enhanced photograph.

3) On the loom, warp (vertical) threads were coated with raw starch to make weaving easier. The starch kept the delicate linen yarn from fraying and made it easier to pass the shuttle with the weft yarn over and under the warp.

4) After weaving, the starch needed to be removed. To accomplish this, the cloth was washed in suds of soapwort.

How do we know this? There is, on the outermost fibers of the cloth a clear washing residue: a thin coating of starch fractions and the various saccharides found in soapwort: glucose, fucose, galactose, arabinose, xylose, rhamnose, and glucuronic acid.

Such a residue is normal in soap washing, even with rinsing. The residue is an evaporation concentration that forms on the outermost fibers of cloth during air drying. It forms on both sides of the cloth.

The residue is so thin it is difficult to see with an ordinary microscope. But we can see it with phase-contrast microscopy or a scanning electron microscope.

We don't know why but in places this residue has turned brown. It has turned into a caramel-like substance. And it is the brownish color, here and there, that makes up the image we see on the Shroud.

Of this we can be certain: the image is not paint and the polysaccharide residue is not is not a photo-sensitive emulsion.