Discarding acetate microfilm masters

>We have commenced a project to create new polyester microfilm
>masters of collections for which we hold prime preservation
>responsibility (we own the master). The new polyester master is
>created via direct contact copying from the original acetate camera
>master. It is not possible to refilm these collections. This means
>that the new polyester master is a second-generation film. The issue
>I am grappling with is this: Should we discard the original
>cellulose acetate camera master?
>
>Issues to consider:
>
>    *   is it a problem to have only a second-generation master if
>        the first-generation is discarded?
>
>    *   how can I be confident that the new polyester master is as
>        good a copy as can be achieved?
>
>    *   justifying the resources needed for ongoing monitoring of
>        vinegar syndrome
>
>    *   rationale for keeping acetate masters when we know they will
>        eventually disintegrate from vinegar syndrome
>
>    *   rationale for discarding the acetate masters when they are
>        the closest thing to the original that we have

At University of California, Berkeley we also have a program for
inspection of old acetate negatives dating back 50 or 60 years.
Although some of these rolls have the vinegar odor and test positive
for low levels of acetate deterioration (with test papers), our main
purpose in this activity has been to identify redox image
deterioration, otherwise known as "microdots."  Brittleness and
other forms of deterioration are not evident; the films are now
stored under environmental controls and many are used to fill
requests for duplicates, without complications.

I can partially address your questions based on our experience with
this, since we have used both contact printing to create polyester
negatives, and refilming on modern materials where the original item
is available.

You ask how you can know whether the new duplicate negative
constitutes adequate preservation of the item.  The simplest way to
do this is by direct comparison through inspection of the two
negatives, that is, first and second generation. Where test objects
such as resolution charts were included in the filming this may be
done fairly objectively: depending on the condition of the contact
printer there may be no noticeable loss or there may be the loss of
one or two line-pair patterns.  In the end, however, it is probably
better to make the comparison subjectively, looking particularly for
the loss or degradation of fine line or faint characters and
"bleeding" or irradiation resulting in poor rendition of bold or
thick line.  Since the purpose of any printing master is to create
copies, you might do well to make periodic comparison test positives
from each negative.  In the positive made from the new negative, has
any information "dropped out" or become difficult to decipher?

It is important to use care in the duplicating process, in order to
ensure the optimal printing negative.  In particular both
low-contrast and high-contrast direct duplicating film is available
and the choice must be made carefully. Then the film must be exposed
and developed for appropriate density levels and image
characteristics and of course processed and stored according to best
practices.

All that said, I don't personally like the idea of discarding
original camera negatives for the very reasons you suggest, and also
for the reason that where preservation is concerned, 2
resources--particularly when they are stored remote from one
another--are better than one.  Nonetheless, a large project
duplicating historic news film for a national digitization project
indicates to us that, with sufficient care duplicate negatives may
be produces with adequate detail.  And in some cases the duplicating
may have the effect of improvement or enhancement to apparent image
quality and reproducibility.

I hope this reply, though not complete, was of some use to you.

Charles Stewart
Sr. Photographer
head, preservation microfilm lab
Pres. dept., U.C. Berkeley library.


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                  Conservation DistList Instance 20:17
               Distributed: Thursday, September 28, 2006
                       Message Id: cdl-20-17-003
                                  ***