halftone

Halftone

The images, closely examined with the aid of microscopes and microphotography, appear similar to halftone images. It is easier to understand monochromatic halftone and since that shroud images are monochromatic, meaning they have only one color, we will ignore color images. Halftone, in the monochromatic sense, simply means that all the different shades of a color in a picture are produced from the quantity, size and spacing of tiny bits of a single color in any area of the picture.

The most common monochromatic halftones are black and white pictures in magazines and newspapers. Look closely at a picture in a newspaper and you will see that all the shades of gray are achieved with dots of black ink only. Halftone is also the way black and white pictures are printed on inkjet printers connected to home computers. With such printers, every shade of gray is produced by minuscule droplets of black ink. Where there are more droplets of ink the printed image is darker; where there are fewer droplets the image is lighter.

One Straw-Yellow Color

On the shroud, the images are halftone straw-yellow and white, meaning the shade of straw-yellow from its darkest parts to it lightest parts are made up of bits of one straw-yellow color. The term pixel has often been used to describe this. It’s a wonderful word but it is a confusing word, just like the word salt. You add salt to soup to enhance the flavor. But when the cook hasn’t added enough salt you say to someone, “Please pass the salt.” You should say, if you want to be precise, “Please pass the sodium chloride.” You certainly wouldn’t want to sprinkle too much magnesium sulfate commonly known as Epsom salt on your food unless you want a very effective laxative.  And you certainly wouldn’t want to sprinkle lead diacetate on your food to make it taste saltier, for it tastes sweet. You also wouldn’t use it anyways because it leads to slow and certain lead poisoning. For centuries, before anyone knew better, lead sugar, as it was sometimes called, though it is really a salt, was used as an artificial sweetener.

One Color, Different Density

That was a new aspect I had not considered. To see what Rogers meant by essentially identical spectrum-wise but different density-wise we need some lemon Jell-O. On a sheet of white paper put a very thin slice of the wiggly stuff on the paper. Beside it put a thick slice. Both slices have the same color but the thicker slice looks darker. This adds another element to the visual blending.

So not only are the images negatives (though not photographic negatives), not only are they height-fields, they are halftone or pixel formed at a fiber level. The best that we can say is, “that’s funny,” for all of these things so far defy logical explanation. And it doesn’t stop there.

The images are decidedly the result of a selective, color producing chemical change along distinct lengths of some of the cellulose fibers of the linen. Chemists who examined the fibers described the chemical change as an oxidation, dehydration and conjugation of polysaccharides (long-chain sugar molecules). It was once widely thought that this was a chemical change to the fiber itself, not unlike the oxidation and dehydration that takes place as linen turns yellow with age.  But Rogers believed he found a clear, ultrathin sugary coating on the fibers. He called it an impurity layer. The yellow color of the images, he thought, was caused by a chemical change to the impurity layer and not the fibers themselves.

Visual Blending

Like a playful Georges Seurat painting, the images on the Shroud emerge from discrete little bits of color in all the right places on the cloth. But unlike a cheerful and colorful Seurat, there is only one color in the Shroud's images. It is a single shade of caramel yellow. And unlike Seurat's pointillism, the bits of color are microscopically tiny. When we look at the Shroud, what we perceive as different shades of yellow is mere visual blending. Where there are more or larger bits of yellow the image appears darker. Where there is less yellow, the image appears lighter. Pixels, a word that means picture elements, is one way to describe the bits of color. The image on the Shroud is like a halftone photograph printed in a newspaper or a grayscale photograph printed in microscopic-size droplets of black ink on an ink-jet printer.

Very much unlike a Seurat, the image was not painted. Many tests including visible, ultraviolet and infrared light spectrometry, x-ray fluorescence spectrometry, and direct microscopic viewing of the Shroud confirm that the images were not painted despite the fact that Walter McCrone, a noted microscopic analyst found iron oxide and mercuric sulfide, both used in paint pigments.