Tinted glass plate negatives

I am scanning a set of 8x10 dry plate glass negatives dating from
1910-1937.  We are scanning them to create positive digital
"prints". In some cases the whole plate or selected areas have been
painted on the emulsion side with a transparent deep magenta
material.  I am guessing that it is a way of lightening areas of the
resulting print.  I would like to know if anyone on the list is
familiar with this practice.  Do you know the compound used?  The
plates covered with the tint have lessened contrast overall.  Would
this be the original intent, or would the tint have a different
effect in the photographic developing process?  I would like to
achieve the most loyal scanned "print" intended by the photographer.

Deborah Tint


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                  Conservation DistList Instance 25:45
                   Distributed: Sunday, April 8, 2012
                       Message Id: cdl-25-45-014
                                  ***