Ethanol soluble adhesives

We have recently received many items from the elections in South
Africa. Among them are some posters mounted to masonite. We tried to
soak them off the backing using quite hot water and then used
enzymes in mild water, and then tried steaming. They just didn't
want to lift off. Then we used ethanol and they lifted off
beautifully.  There isn't any sticky residue and I was wondering what
could have been used as the mounting material?

Deborah Howe
Collections Conservator
Northwestern University Library
1935 Sheridan Road
Evanston, Il  60208
708 491 7607

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                  Conservation DistList Instance 9:48
                 Distributed: Monday, December 11, 1995
                        Message Id: cdl-9-48-012
                                  ***