I keep reading about banding but I don’t understand what caused it and why it is significant.
Linen in the first century, in the Middle East, was hank bleached. It was an imprecise method resulting in some yarn being whiter and some slightly darker or off-white. This resulted in variegated patterns in linen cloth as different hanks of yarn were fed into the loom. See contrast-enhanced photograph of variegated patterns
Some of the bands of different shades of white (now perhaps more yellowed and browned with age) are narrow and some are quite wide.
The variegation, or banding as it is sometimes called, produces a visual background noise pattern that alters the way we see things on the Shroud.
The face of the man of the shroud is gaunt. That is a common observation. The nose is narrow, eye sockets exceedingly deep, the hair seems to fall straight. At least that is how is seems. Look carefully and you will see that the gaunt appearance is the result of dark vertical bands on each side of the face on the outer part of the cheeks. There are faint, less perceptible bands on each side of the nose and a horizontal band across the eyes, as well.
Fourier transform filters can be used to mathematically find these bands and minimize their effect. Notice how filtering seems to change the shape of the face and nose and makes the eyes look more normal. The hair is less forward. It doesn’t actually change the shape of the face; it merely minimizes the background noise and allows details to emerge.
It is very unlikely that the linen cloth used for the Shroud was produced in medieval Europe. Such cloth was field bleached after weaving. Medieval European linen was not hank-bleached. Instead, the woven cloth was soaked in hot lye solution, washed, soaked in sour milk and washed again. Other ingredients, like cattle urine were sometimes used, as well. Following this treatment the cloth was spread out in fields in the sun. This process eliminated variegation.
To my way of thinking banding provides strong evidence that the cloth is not medieval. It also provides a strong argument against opaque imaging methods. That would certainly be some paints, the metals produced from photosensitive salts. I don’t know about scorching. I rather suspect that it would not prohibit very light scorching.
The most significant aspect of banding is realizing that the man whose image appears on the shroud may not have looked like we think he does: