Sealing display cases

Does anybody have any good ideas about ways to seal gaps between
plates of glass making up a display case?  I have a particular
problem with one case in which the gap between the front panel and
the side panel is up to 3mm wide.  Unfortunately, the sealing method
used must be easily reversible as access to the case is by the
removal of the front panel. Any suggestions greatly appreciated.

Sarah Lewery
Conservator
Churchill Archives Centre
Churchill College
Cambridge CB3 0DS
+44 1223 336153

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                  Conservation DistList Instance 12:75
                  Distributed: Tuesday, March 23, 1999
                       Message Id: cdl-12-75-014
                                  ***