Glass plate negatives

We have here some dry-plate (collodion) glass negatives, of various
sizes, that exhibit lifting of the emulsion layers off the glass
support, probably due to our low relative humidity.  The suggestions
I've read for treating this problem basically involve carefully
edging a mat board up over the flaking area so that the dislodged
pieces are fitted and secured into position by sandwiching the plate
between that and another mat board.  The problem is that then the
plate can't be printed.

I wonder if anyone knows of another solution that would allow the
plate being printed again.  Our photo archivist and myself
speculated on a *glass* sandwich arrangement using filmoplast (or
Tyvek tape), like that used for broken or cracked plates.  It seems
that this method would affect the same protection and placement of
the emulsion, but would allow for subsequent printing.  Any thoughts
or experience with this?

In addition, several of the negatives have become soiled on the
surface of the emulsion layer.  Does anyone know of an emulsion
cleaner that they would suggest for such a case?

Noel A. Carmack
Book Conservator
Merrill Library
Utah State University
Logan, Utah

                                  ***
                  Conservation DistList Instance 9:30
                Distributed: Friday, September 29, 1995
                        Message Id: cdl-9-30-011
                                  ***