Argon gas Bleaching and redevelopment Mineral light Audio tape preservation

I'm waaaaaaaay behind but I'll throw in my 2 cents worth anyway.

I agree with responses to the question about argon gas and albumen
prints. Argon is a pretty inert gas and should cause no other problem
other than excessive drying of the albumen.  Of course, humidifying the
argon will help to prevent this problem.  I might point out that argon
has been successfully (as far as anyone can tell) used to help preserve
the "oldest photograph" -- down at the Harry Ransom Humanities Research
Center.  Barbara Brown could say more about this.  In addition, although
argon, like all gases, suffers from diffusion through small holes, it is
still much better (slower diffusing) than lighter gases such as helium.
(We had to measure relative rates of nitrogen, and helium diffusion in
kinetics class, but it is reasonably apparent when you compare how long
a balloon blown up by mouth stays inflated vs a helium filled balloon.)

Hilary has been kind enough to write a piece about bleach and
redevelopment, so I won't repeat.  I might try to clarify one part about
the mechanism (since I think this group is technical enough.)  Entropy
on the small scale can be reversed by the addition of energy.  Consider
my apartment.  It is approaching a state of maximum entropy although it
can be reversed if I clean it up (ie put energy into it.)  However,
there is a limit to what a small amount of energy can do.
Reconsolidation of filaments amounts to raking up a lawn full of leaves
into 5 piles and then scattering them again.  As long as the leaves
haven't been scattered too far we can rebuild the 5 piles. Note that the
location of each pile is not necessarily exactly where the original
piles were, but if there is enough evidence of where the piles were we
can be close.  Also, the leaves in the pile are not necessarily exactly
the same leaves that were there before nor are the piles exactly the
same size and shape as the original leaves.  Finally, some of the
original leaves may be missing.  You and the rake represent the chemical
energy of bleach and redevelopment.  On the other hand, if there is no
longer any sign where the original piles were and/or if the leaves have
been scattered across 3 states,  then there is very little likely hood
that the piles can be rebuilt with the energy available (you and the
rake.)  Thus, small amounts of fading and staining can be somewhat
reversed by chemical treatment, but red spots, mirroring and detail loss
(due to excessive fading) can't be.

One other note about the effects of bleach and redevelopment.  While
doing research into B & RD at the Canadian Archives we were also
interested in showing silver migration.  Ultimately we ended up using
one of the "recommended" bleach and redevelopment processes to strip the
gelatin emulsion off of degraded photographs to show the "ghost" image
on the baryta layer (below the emulsion layer).  Also Chlorox (Javex for
any Canadian readers) (another bleach) is very effective at dissolving
both the emulsion and the the baryta layer off photographs.

Regarding the use of a mineral light (UV light) on manuscripts --
exposure may be reduced if you use UV photography.  This technique is
often used with paintings (also IR and X-rays).  It's very much like
Bill Cosby complaining about children leaving the fridge door open while
they decide what they want.  He says that they should take a Polaroid of
the fridge contents, close the door and then decide what they want.
People with questions about the technique may want to contact a painting
conservator.  I also know that Brian Thurgood at the Canadian Archives
(with a degree in photographic technology) would also be useful.  (He
can be reached at 613-996-1573 or at

Conservation Treatment Division
National Archives of Canada
Room B-145
395 Wellington St.
Ottawa, ON
Canada
K1A 0N3

    **** Moderator's comments:   I think I probably have some decent
    notes on UV photography from Tom Moon's photodocumentation course at
    the Getty.  If you want a (hard) copy, let me know.

Finally I am recommending to Peter Hirtle, who inquired about tape
preservation to talk to Bill Storm at the Belfer Audio Lab and Sound
Archive at Syracuse University.  Also Bill O'Farrell and Roger Easton at
the Canadian Archives deal quite extensively with tape preservation
problems.

-Doug

    **** Moderator's comments: I'm told that Bill Storm's email address
    is WDStorm%rodan.bitnet.  If you talk to him, maybe you could entice
    him onto the DistList.  (Same for the others, of course, if they are
    on the Net

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                  Conservation DistList Instance 5:15
                 Distributed: Saturday, August 17, 1991
                        Message Id: cdl-5-15-002
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