Ferrotyping

Is it safe to place photographs in direct contact with their
mylar/melinex enclosures? I have heard of an effect called
"ferrotyping" which can happen to gelatine-coated
photographs--apparently some sort of change in the appearance of the
surface. Can anyone fill me in - what is "ferrotyping", and is it
only a problem for gelatine coated material (which should then
presumably have a barrier of a suitable safe paper.)

How do other photo archives deal with this?

Basically, we do not want to have to interleave thousands of photos
unless we have to. The storage conditions are pretty good, stable
without too high a RH. Thanks

Mark Clarke
+44 171 277 1633

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                  Conservation DistList Instance 9:42
                Distributed: Thursday, November 16, 1995
                        Message Id: cdl-9-42-007
                                  ***