Earliest Modern Mention of Glued Linen Armor?

[Creon01]

It is so odd that the French author would be so precise and we can't discover his source.

Well, we can!  The 18 layers and the salt and vinegar come from a Latin summary of Nicetas Acominatus, who wrote in the 13th century CE and described the armour worn by the Franks during his lifetime.  The lack of protection comes from Pausanias' tourist guide in the 2nd century CE (Pausanias 1.21.7).  You can find all of these sources in the footnotes to Margharita Gleba's article in Wearing the Cloak: I think she has put a free copy online.  

And for what it is worth, I have read many guild rules and lists of expenses in making linen armour in the 13th and 14th century, and none of them mentions salt or vinegar.  So a chronicler like Nicetas Acominatus is not really a good source.

Right, I mean why would that reputable 19th century author apply that information specifically to the ancients?

Wearing the Cloak is an excellent book by the way and everyone should have a copy.