Here is my hunch. It is not a shroud, as in, it is not a piece of cloth that was used at some point to envelope a dead body. But it is not a forgery per se, either.

What do I mean?

I think this is what happened: at some point, after christianism had already settled and there was known iconography, someone made a sculpture of the crucified Jesus. Said sculpture had to be transported somewhere, so someone covered it in cloth, then maybe baled it in with straw or cotton or whatever as protection.

Then it was forgotten for a century or two. Long enough for the sculpture to leave a clear impression on the cloth.

Bam. No need of supernatural whatchamacallits, no need either for advanced forgery techniques. Just a statue and a bit of time.

Extraordinary claims require extraordinary evidence. The museum should counter-offer Mr. Rolfe a billion dollars if he can prove how HE thinks it was made.

And let's be real about this: they could produce an exact replica and his reply would be "well MY imaginary friend says you're WRONG".

Carbon dating has shown long ago that the cloth is only around 1000 years old, not the 2000 years old that would be necessary for the Shroud to be genuine.

The 'how' is irrelevant against that evidence.

Now you just need to figure out how they made it 1000 years ago and the million is yours!