We are supposed to believe that not only did this hypothetical artist already know this, but that he used it only once and never used the technique again.
I will be the first to grant admiration to alchemists... it is they who established the modern science of chemistry and the experimental model. They were the first to start sharing techniques, reporting what did and didn't work, and what results they got trying various things. They systematized the naming of chemicals (at least they had to agree what ingredients they were using)... but I sincerely doubt that any of them had the polymath abilities and range of knowledge that must be attributed to the hypothetical creator of the Shroud of Turin.
The motives of those who seek to "discredit" the shroud or to prove it a "forgery" are varied.
Some are Christians who fear having their belief that Faith without proof is enough or that it is somehow superior to belief because of proof. . . and that any offering of proof will diminish the value of their belief. Still others are of the opinion that the Gospels they are reading in English have been translated from the Greek by God... and that the more precise meanings of words in Greek that have no English equivalent can be ignored in favor of their colloquial understanding of English. As a result they believe that any Shroud that is not as described exactly as it is in THEIR version of the Bible, it must therefore be a fraud... and a temptation of the Devil. Anything they can do to prove it a fraud is fighting Satan.. . and a good thing.
Others fear that ultimate proof that a man named Jesus did indeed live and suffered the indignities and death described in the Bible would then require them to reconsider their cherished unbelief in any Biblical report. Even the proof of Jesus' historical existence is threatening to those who prefer not to be judged by any ultimate authority.
Some, like John Dominic Crossen and the other members of the Jesus Project, are self styled deconstructionists who have convinced themselves that their opinions are far superior to the literal words of the Bible. They prefer to place their arrogant intellectual opinions of Biblical events on a pedestal as an example of modern critical thinking instead of what they actually are: a house-of-cards exercise in nose-picking. A Shroud that show them to be blow-hards would upset them immensely, and probably force them to find other productive work... for which they are uniquely unsuited.
It is amazing to see supposedly sane, open minded "scientists" abandon proper scientific procedure and choose to ignore peer-reviewed work published in scientific journals in favor of popular books written by non-scientists (Joe Nickell) and the old discredited work published unethically in vanity press magazines (Walter C. McCrone) simply because it disturbs them that something religious just might have some validity. They will accept almost any explanation, regardless of logic, if it meets their prejudices.
To show it could have been created by any means at all that is non-miraculous, diminishes the possibilities of all of the above.
From your comment, it appears you have abandoned your position as a shroud critic... I am curious... how and why did you change your position?