[quote="ReneZ" pid='68624' dateline='1752211214']
[ the stains on the inside of the front cover] are definitely caused by the wax on the Marci letter
[/quote]

Perhaps those ones... However, from the way the stain on f103v seeped through the vellum and continued on and through the adjacent pages, I believe that the staining matter had a substantial liquid component. 

I presume that the stuff was blotted and rubbed off soon after the accident, and I can't see candle wax or tallow doing that.  

Besides, candle wax or tallow is white, and I don't thhink it could become deep rusty brown even after a century.

The stuff that caused the Big Rusty stain was spilled on f102v1 or f103r, then the book/quire was closed so that the stuff was squished over that large area of f103r and f102v1 (~35 mm wide).  A small separate drop (~5 mm wide) fell due East of it.  From there it seeped through folio f103, created a fuzzier version of the stain on f103v, pooled between that and f104r leaving a smaller stain on the latter, with sharp edges, and a bit still seeped through leaving a fuzzy fainter stain on f104v. In the other direction, the stuff got through folio f102 and made a stain on f102r1. That folio evidently was folded in at the time, so the stuff stained f101r2 by contact and got through that folio again staining f102v2.

The Small Rusty stain (~15 mm wide on f103r), S by SE of Big Rusty,  did something