Bleaching and redevelopment

This is a response to Michale McCormick's inquiry about "Restore", a
bleach/redevelopment product.  It was prepared with a great deal of
technical assistance from Doug Nishimura, and will appear in more or
less the same version in a forthcoming issues of the Society of Georgia
Archivists' Newsletter.

The short answer to Michael's question is NO, neither "Restore" nor
other bleach/redevelopment products should be used on holdings of
permanent value.  Doug Nishimura, formerly of the National Archives of
Canada and now at the Image Permanence Institute explains that while
rebuilding an image may be theoretically possible for developed out
papers, this process is not feasible for printed out papers.  This
distinction between processes reminds us that it is imperative to know
the nature of the materials with which you are dealing prior to
contemplating any type of "treatment."

Roughly 8 years of research into bleach and redevelopment has been done
at what is now called the Conservation Research Division at the National
Archives of Canada.  'Bleaching' /redevelopment is described as "a very
risky business." that is NOT recommended.  Fading of developing-out
prints occurs because of oxidation, as silver particles on filament
bundles are converted from a silver metal into ions.  These ions are
mobile in gelatin and can drift from their originating filament.  Ions
may convert back to silver metal as colloidal silver or may bond with
other chemicals in the gelatin to form insoluble and non-mobile silver
salts.  Doug points out that the laws of nature do not allow migrated
silver to return exactly to its original location, BUT if enough of the
filamentary bundle is present, and in close enough proximity to the
migrating silver, reconsolidation is a THEORETICAL possibility.

If the silver filaments have been severely broken (high degree of
fading) or if the silver ions have migrated too far from the filament
(mirroring and red spots) bleach and redevelopment will be ineffective.
Because gelatin is sensitive to oxidants and alkalines in solution,
bleaching or a combination of bleaching and redevelopment can literally
strip off the image layer of the photo, permanently destroying the
photographic image.

Doug cautions that bleach/redevelopment rarely reforms the original size
and shape of the silver filaments and therefore rarely recreates the
darkness (density), contrast, and tone of the original image.  His point
raises serious ethical questions about altering artistic intent or
intrinsic value of the photographic image.  In addition, the stability
of the photographic image may be altered as a result of this type of
treatment.

In general, it is best for the buyer to beware when thumbing through
catalogs.  From a preservation standpoint, many products can do much
greater long term harm than good.  As a rule, it is best to approach
chemically irreversible treatments conservatively, exploring other
non-intrusive options (such as proper housing and storage) first.

While the Image Permanence Institute has not directly investigated
"Restore," the Institute has studied a number of issued of direct
relevance to the preservation community, and makes that information
widely available through publication or inquiry.

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                  Conservation DistList Instance 5:14
                  Distributed: Friday, August 9, 1991
                        Message Id: cdl-5-14-003
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