Removing permanent ink from paper

I am a paper and book restoratrice, I'm used to working with old
drawings and maps. But now a client came to me with Popp maps where
permanent ink has been used on the back. I tried all solvents that I
know that are used in todays ink, but with no good result. I tried
all sorts of applying means such as compress, suction table, even
immersion in solvents. Has anyone experience with this or can anyone
help me in my search?

Elke De Smet
Paper and book conservator
Papier- and boekrestauratrice
Koningin Astridlaan 61/21
9230 Wetteren
Belgium
+32 476 332556


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                  Conservation DistList Instance 25:6
                 Distributed: Wednesday, July 13, 2011
                        Message Id: cdl-25-6-011
                                  ***