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Subject: Paint for microfilm cabinets

Paint for microfilm cabinets

From: Lisa Mibach <perygrine>
Date: Sunday, June 19, 1994
"Baked enamel" should probably  be avoided: this term actually means any
paint which is heat cured, and is usually alkyd paint. I have an article
from 1931 describing the corrosion of electrical wiring by alkyd paint;
my old-fashioned painter tells me that only a fool would use alkyd paint
around wiring.

In 1980 I encountered significant corrosion on coins and medals in a
damp vault painted with alkyd paint, and worked with a local paint
company to develop a paint based on Rohm and Haas AC33 acrylic resin
rather than alkyd resin. This seemed to work ok.

One of our departments also ordered a large number of "end of fiscal
year" cabinets which were spec-ed only as "baked enamel"...these arrived
smelling highly of solvent, and the paint came off on a swab with
Stoddard's Solvent (probably due to poor stoving).  I installed metal
test coupons, and, frustratingly, nothing happened for 18 months: little
change in silver, copper, or lead. Then, suddenly, the lead turned into
powder on the bottom of the case. Long induction time, I guess, but
certainly an indication of  the outgassing organic acid vapors generated
by the drying oil base of alkyd paints.  Even though you are not storing
metals (except for the silver, of course), lead is our "canary" and
indicates problems of acid outgassing sooner than most other materials.
(I also saw an unusually high amount of textile fiber on the bottom of
wooden textile drawers in these cases, but was not able to carry out
thorough investigations--I do, however suspect gaseous acid attack on
vegetable fiber textiles.)

Since then Delta Design Cabinets in Topeka Kansas pioneered the use of
powder paints. these have the advantage of not using solvent, which can
take years to evaporate from a paint film, especially if the surface has
been dried first with heat curing. It appears that these powder paints
are available as polyester,  epoxy, and a hybrid of the two. Skip
Dickinson, the founder of Delta, chose the hybrid because it was the
least uv sensitive (indicating a potential chemical instability, even if
one does not expect to encounter uv in storage), but you would probably
want to conduct your own investigations into the chemical stability of
the powder paints available from local painters.

Lisa Mibach

                   Conservation DistList Instance 8:3
                  Distributed: Tuesday, June 21, 1994
                        Message Id: cdl-8-3-004
Received on Sunday, 19 June, 1994

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