Hi Teresa,

The powdery substance may not be mold!  On the other hand, it may well be. Keep the photograph enclosed  separately and keep it in a
low RH environment temporarily while the substance is analyzed to identify what it really is. Do not do anything without analyzing
it first: without that knowledge, the proper treatment will not be able to be devised. Keep it isolated so that the suspected mold
spores will not contaminate other objects in your collection! THIS IS IMPORTANT.

Then, visit the AIC WEB site http://aic.stanford.edu: there you will find a list of trained  conservators
who are knowledgeable about the proper methods of analysis and treatments of photographs as well as mold treatments. I am relatively
sure that there should be a
qualified knowledgeable conservator in your area.

As this is a historically significant photograph, I would beware of "garden wisdom" and "cookbook" solutions as they could invite
future
degradation of these objects.

Regards,

Jim Moss
Horological Conservator

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