Looming above all other issues is what physicist Paolo Di Lazzaro calls “the question of questions”: how the image was produced, regardless of its age. Every scientific attempt to replicate it in a lab has failed. Its precise hue is highly unusual, and the color’s penetration into the fabric is extremely thin, less than 0.7 micrometers (0.000028 inches), one-thirtieth the diameter of an individual fiber in a single 200-fiber linen thread.

Di Lazzaro and his colleagues at Italy’s National Agency for New Technologies, Energy and Sustainable Economic Development (ENEA) conducted five years of experiments, using state-of-the-art excimer lasers to train short bursts of ultraviolet light on raw linen, in an effort to simulate the image’s coloration. The ENEA team, which published its findings in 2011, came tantalizingly close to approximating the image’s distinctive hue on a few square centimeters of fabric. But they were unable to match all the physical and chemical characteristics of the shroud image. Nor could they reproduce a whole human figure.

The ultraviolet light necessary to do so “exceeds the maximum power released by all ultraviolet light sources available today,” says Di Lazzaro. It would require “pulses having durations shorter than one forty-billionth of a second, and intensities on the order of several billion watts.”

If the most advanced technologies available in the 21st century could not produce a facsimile of the shroud image, he reasons, how could it have been executed by a medieval forger?