[Design of Marci Letter]

[Jorge_Stolfi]

Here is the entire length of the tab in the picture you took on the light table, with the brightness and contrast played with to be able to see it as clearly as possible (I think, others could play with this image themselves, and maybe get more out of it):

With my superior pareidolia, I think I see the thin dark irregular edge of a water stain, running along the tab fold, about 1 cm above t.

If real, that could be water from the paste that seeped through the tab and onto the letter, that was presumably folded over the tab while the paste was still fresh.

Or perhaps water that was applied to the tab in order to soften the glue and release the letter from the cover, when the book was re-bound.

Before the invention of PVA ("Elmer's glue"), nitrocellulose, etc., I suppose that "glue" in household and scribal contexts should have meant either a paste of flour and water, or a thick solution of gum arabic.  The former would release water that would seep into the paper; but would probably have been eaten by insects or molds long ago.  The latter would not have seeped into the paper, but may have survived better, and would probably have been softened easily by wetting.

By the way, I can't imagine Marci attaching the letter to the book by sewing it into the binding.  That tab surely was meant to glue it somewhere on the book (or paste it, if we are to distinguish the words).  I suppose that the book had been bound well before Barschius got it, and I don't see why Marci would re-bind it.  And I doubt very much that the Jesuits (or whoever re-bound the book after Kircher) would have decided to incorporate the letter into the new binding.

All the best, --stolfi