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Subject: Acetate negatives

Acetate negatives

From: Doug Nishimura <dwnpph>
Date: Tuesday, April 23, 1991
Well, the short (and blunt) answer is "no".  Once the film starts to go,
there is nothing that you can about it, although cold, dry conditions
will probably help.  We haven't (and may not be able to) study the
inter-relation between degradation in various states and cold storage.
The problem is that there are 4 main reactions - hydrolysis of the side
groups, hydrolysis of the polymer chain, oxidation of the side groups,
and oxidation of the polymer links.  Under humid conditions hydrolysis
is the predominant reaction mechanism while under dryer conditions,
oxidation is more important. Of course, oxidation is a much slower
reaction than hydrolysis even when it is predominant.  (Please ignore my
spelling.)  The relative rates of hydrolysis causing a) chain scission
and b) glycosidic cleavage (or deacetylation and depolymerization
respectively) depends on the storage condition.  Even the number of
layers of gelatin has an effect.  Often sheet films are coated on both
sides with gelatin (one is the emulsion and the other is the anti-curl
layer.)  Double-, single-, and un-coated film bases all behave
differently with respect to the rate of depol. vs deacet. at different
humidities. The other complication is that the deacetylation
(de-esterification) reaction is autocatalytic while the glycosidic
cleavage is not.

In short, we don't know how cold storage will balance out with the
various rates of deterioration.  However, cold st. seems to be the best
bet although the stress of taking the negative out of cold storage may
cause severe channeling.  BTW, in the next project we will be looking at
the change in emulsion adhesion with deterioration.  The Florida State
Archives made some good observations that showed that bond adhesion
often goes long before it shows up as channeling.  They had taken some
film out of storage for copying and it literally started channeling
before their eyes.   They took a second sheet out and every hour, drew a
pencil line around the edge of the channeling lines (ultimately, the film
looked like a topographic map). It only took a few hours for very severe
channeling.  The bond between the emulsion and the film base gave out
long ago, but the final separation was brought about by the stress of
changing the storage conditions.  (The diff. between the storage and
office conditions were really not that great, however.) ....

Sorry the news isn't better.

                  Conservation DistList Instance 4:56
                  Distributed: Sunday, April 28, 1991
                        Message Id: cdl-4-56-012
Received on Tuesday, 23 April, 1991

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