- Thu Jan 31, 2019 5:35 pm
Hope you don't mind if I jump in on this one, as I know this (extremely difficult) question quite well.
The flaw behind the argument is one of Incompatible Assumptions, in that the titanium in the ink was somehow used to imply both a rarity and commonality, and both of those implications could not be true together.
The rarity, or it being "extremely restricted" comes from the idea that since the Gutenberg Bible and B-36 both had titanium in their ink, but no other of the 15th century books did, that both Bibles came from the same printing press. That's a pretty sure sign for extreme restriction as it implies that the titanium was so rare, that if only two Bibles out of the "numerous other" books examined had titanium in their ink, they must have originated from the same source.
The lack of restriction in the presence of titanium involves the Vinland Map. This map does have titanium in its ink, but its age was originally doubted as being from the 15th century because of that fact, which connects to the idea that no other of the "numerous" documents of that time were found to contain titanium in their ink. When the author implies that the Gutenberg/B-36 connection allows us to no longer doubt the authenticity (re: age) of the Vinland Map, it's based on the awkward assumption that since Gutenberg and B-36 were that old and had titanium in their ink, then why couldn't the Vinland Map also be that old?
Problem is, the second assumption relies on the idea that titanium must have been common enough in the 15th century that at least two other books had it, so it's no longer a reason to doubt the Vinland Map's supposed age. But that would be inconsistent with the previous line of reasoning that used the rarity, or 'extreme' restriction of titanium at that time to imply the Gutenberg Bible and B-36 must have come from the same printing press.
This is a famously difficult question, but I hope this helps to clear it up!