I defy him to name one reasonable explanation that can possibly explain the images as they are. Here is his problem:
For there to be an image on the Shroud there must be an image producing agent, something that will absorb or reflect certain wavelengths of visible light that is different than the background. That agent might be something that coats the fibers of the cloth, it could be a chemical state of change to the cellulose fibers themselves or it could be a material within the hollow medullas of the translucent fiber. However the core is clear and the cellulose fiber remains unaltered except for a certain amount of dehydration and oxidation resulting from aging and producing some discoloration. There is no appreciable difference in the discoloration or image bearing fibers and non-image bearing fibers.
Thus we are left with the possibility that image agent is contained within a coating of the fibers. Spectrographic examination, chemical tests and microscopy have ruled out the possibility that this coating contains pigments as found in paint, inks, dyes and stains. While trace amounts of some pigments, as contaminants, have been found, nowhere have sufficient concentrations of these been found to form an image that can be seen by the naked eye.
To the contrary, a carbohydrate coating of starch fractions and various saccharides has been found coating fibers on the outer topmost crown fibers of the cloth. In other words the coating is superficial. This coating has been observed to be between 180 nanometers and 600 nanometers in thickness. In terms of thickness this is comparable to the scratchproof coating used on eye glasses. This coating can be removed from the fibers with adhesive or with a reducing agent such as diimide.
In diverse and discontinuous places, on the superficial surface of the Shroud, the coating on the fiber has undergone a chemical change that has changed its visible light absorption properties. It has become straw-yellow. Where there is color, the color is the same color from one fiber to the next. There is very little variance in luminescence from one fiber to the next, as well. The resulting composite image of many different visible shades is the result visual blending of the quantitative density of colored fibers. Often referred to as a pixilated or halftone image; it is more accurately visual shading like the hatched shading of a pen and ink drawing, but implemented at a microscopic level. Individual fibers are approximately 13 micrometers in diameter (roughly 15 percent that of a typical human hair). In other words, a selective chemical change has occurred that has produced an image.
The carbohydrate coating is easily explained by the way that linen was produced in the first century. We need only turn to Pliny the Elder for a detailed explanation. During weaving a crude starch was applied to the yard to lubricate it and prevent fraying. After weaving, the cloth was washed in suds of Saponaria officinalis (a natural soap) and dried lying flat across bushes. Residual chemicals from the washing concentrate at the evaporation surface, forming the colorless carbohydrate layer on the outermost edges of the top fibers in the thread. Concentration at the evaporation edge is a very natural phenomenon when cloth is air dried. This coating is chemically reactive.
But what caused the chemical reaction that formed the images. Any number of speculative possibilities warrants consideration. These include chemicals in liquid or gaseous form, corona discharge and various forms of radiation including heat. The most promising of these, so far, chemically, is that heavy amines produced by a dead body reacted with the coating, a amino-carbonyl reaction (Maillard reaction). That such a reaction will take place within a few hours is indisputable. Coloration will take place. But will that explain the quality of the image? So far, alone, the answer is no. Scientists recognize that the image forming process must be a complex system of many factors including body chemistry, residual body heat, ambient temperatures and humidity, the lay of the cloth over the body.
But that is the problem, as well. Is it a lucky fluke that the images are so visually correct? A truly natural explanation requires that a chemical reaction starts and ends. The reaction must end sufficiently late for there to be discernible images. And, it must end early enough that the images are not oversaturated. Analysis of the images shows no saturation plateaus. Timing is everything. In photographic terms this is correct exposure.
It is not just correct exposure that is at play here. Good focus, suitable contrast and smooth and realistic gradations between light and dark areas are also important. (Resolution is better than 0.4 mm at a distance of 1.1 cm indicating the image production mechanism must be highly anisotropic). This is further supported by the fact that when the densities of the “pixels” are plotted, a three-dimensional orthographic image develops. There is nothing like this in art or photography.
Is it serendipitous that the highlights and shadows of this chemograph appear as though created by reflected light? This visual quality is essential for our minds to be able to see the images as realistic pictures with perceived three-dimensionality?
The images are at once like rare and exceptional art, yet so unlike art. They are like subtle photographs and yet so unlike photographs. However the images were formed, the process was quick. The cloth and the body were separated soon. For after about three days, fluidic decomposition products from the body would have stained and damaged the cloth. Soon the cloth would have rotted away. Furthermore, forensic experts tell us, the images show no visible signs of decomposition. This apparent early separation of the body and the cloth opens up a floodgate of possibilities that must be reconciled to any naturalistic explanation.
No matter how much we might marvel that everything for a process might come together in all the right places -- chemicals, ambient temperature, humidity, the drape of the cloth -- and start and stop at the right time, we cannot help but notice something. For until and unless other examples of such images on cloths that survived decomposition in a grave are found, we must say it is unique. The surprise is that this unique and improbable happenstance is not, as mere chance would mandate, of some random person in history.