This means that no paint or dye caused the image; otherwise there would be wicking of the dye along the thread or soaking of the dye down into the fibers below. The yellowing of the fibers can be caused by heat, acid or light. The color change is a dehydrative oxidative process which is the same as the degradation of the cellulose. Think of a vase that has covered a linen cloth for years, and when you remove the vase the cloth is white underneath and the rest of the cloth that was exposed to the light of the sun has been yellowed. These fibers of the Shroud image are all essentially the same light-yellow color. What makes one area lighter or darker to form the image? If one area is darker than another, more of that area’s fibers are light-yellow. The concept can be compared to newspaper print. If you want it darker, put in more dots. Furthermore, these details are the same for both the front and back images. In contrast to what one would surmise, body weight played no role in image formation. The image marks are very superficial as opposed to the blood marks that sink into the cloth, and some even penetrate through to the other side. No one has yet reproduced the Shroud image at this microscopic level.