Image change in photographic negative

Doug Harrison <lab [at] sec__state__la__us> writes

>...  The Louisiana State
>Archives has several large format (8x10) negatives taken on the
>scene of Huey Long's assassination.  On several of them there is a
>shifting of the negative image to a positive one...
>
>What, chemically speaking, is going on here?  Can any treatment stop
>the process?

I think some additional information (send to the list) would be
helpful for potential answerers...

My suggestions:

    *   Type of base material (glass plate, nitrocellulose, etc.)

    *   Is there silver mirroring, or and density discoloration on
        the negative? (If you can upload scanned image/s to the Web
        from typical details of the deterioration I suggest to do
        it.)

    *   A few words about storage/handling history of these
    materials.

Anyway independently from the results of your searching I suggest to
make duplicates to save the recently still existing information
with the best technology as you can.

Balint Flesch

                                  ***
                  Conservation DistList Instance 12:93
                  Distributed: Wednesday, June 2, 1999
                       Message Id: cdl-12-93-006
                                  ***