An important and major conservation project recently took place after Eric White, Curator of Rare Books, discovered fragments of early Gutenbergian printing in a 1483 Venetian publication of Horace in a German binding https://blogs.princeton.edu/notabilia/2017/11/13/princeton-acquires-hidden-gutenbergian-donatus-leaf/. The printed fragments are from a publication of Aelius Donatus. The typeface appears to be the same as that in the Mainz Gutenberg Bible (1455). The bulk of the printing on vellum, which was used as part of the binding’s construction, lay under the front and back paper pastedowns. After discussions between Eric and Paul Needham, Scheide Librarian, and myself, it was agreed that the pastedowns should be and could be safely removed to reveal the printing. The Gore-Tex® damp pack method was chosen to lift the pastedowns. The method introduces moisture slowly into the glue of the pastedown paper in order to swell the adhesive, and in doing so helps loosen its grip on the substrate below. The pastedowns were lifted by carefully and gently pulling the paper away from the substrate below. The vellum fragments remained in place adhered to the wooden boards and were not disturbed. The treatment worked extremely well (fig. 1). The entire process required about 12 hours of slow methodical work.
Fig. 1 A pastedown is shown successfully lifted to uncover a vellum fragment with Gutenbergian printed text. A very slight amount of printing ink offset occurred. This was expected and discussed before determining to lift the pastedowns. The binder, who bound the book, slightly solubilized the ink when he applied wet glue to the pastedown paper and laid it over the printing ink. The glue dried with the top layer of the ink set into the glue layer. There was no way to have avoided this occurrence when lifting the pastedowns.
Ted Stanley, Special Collections Paper Conservator