"It was an expert job using an invisible weave that so closely resembled the original material..."
Does that make sense to you?
It doesn't to me, given the technology that was around in the 1400's and given the technology that examined the shroud in 1988.
That said, I concur that no one can determine how the image was formed.
The actual shroud would be a revered and honored cloth indeed as would any item associated with the crucifiction. I do not doubt that it would have been kept and protected thru the centuries. Other relics like the titulus crucis were hidden away as was the shroud for long periods. That certainly helped its survival.
So it is not unreasonable for it to have survived.
I just found it strange about testing a patched area....
Here is a link to a site with a picture of how threads were interwoven between the old material and new patch.
http://www.factsplusfacts.com/
The invisible weave is a technique done on expensive/precious clothe that has been around quite a while. It is not technologically advnaced it just takes a lot of patience, time and technique born of experience. A weaver/tailor takes the threads in the individual fibres, unravels them and then splices them back together, one thread at a time.
If you have an expensive jacket that gets a clean cut, one could have this done to repair it even today. And it wont even be noticable in strong bright daylight.