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...

I [...] think IPI might know this phenomenon but, in fact, it would
be irresponsible for anyone to make a judgement and/or recommend any
corrective without actually inspecting the negatives.

In my [private] email to you I asked a question pertaining to
viewing method when inspecting (transmitted vs. reflected light). If
it was by reflected light, there is the possibility that the shift
in polarity is only apparent, due to the well-known tendency of
negatives, especially in low-density areas, to take on the
appearance of positives when viewed from certain angles by this
method.  The phenomenon was used as the basis for making the old
"ambrotypes".  The greater effect in the shadow or low-density areas
would account for the patchy or partial nature of the shift.

If the negatives look like positives over a light box (i.e. by
transmitted light), with no evidence of oxidative-reductive
damage--mirroring, colored fogging, etc.--then I wonder if there
isn't some sort of printing/developing out occurring, due to residual
silver salts in the emulsion, resulting from inadequate fixation.
The question also arises as to whether the deteriorating nitrate
base is a contributing factor.

As someone suggested, if the negatives are in a physical condition
to print them safely, the results in paper or film prints would show
you whether they were still serviceable negatives, with the factor
of risk being exposure to light, which may trigger the change, along
with/in addition to heat and humidity.  Printing them to film would
also provide insurance against the loss of the originals.

Refixing and rewashing also come to mind, but with old nitrate
negatives that might be dicey.  There's a chance of the emulsion
coming away from the base, for one thing.  Maybe something like that
could be tried *after* getting good copies from the film.

Hopefully a photo conservator who's very familiar with what you have
will weigh in with something, or even come have a look, which would
be best.

C. Stewart
Sr. Photographic Technician
LPS, U.C., Berkeley

                                  ***
                  Conservation DistList Instance 13:1
                 Distributed: Wednesday, June 16, 1999
                        Message Id: cdl-13-1-003
                                  ***