Cor-ten steel sculpture

Dr. Rust, Thanks for responding to my comments. I don't quite agree
to what you suggest I do, but my sense of the Cons DistList audience
is that those actually interested can find out what they need to
know with or without our exchange.

In many types of chloride corrosion, a small amount of chloride
repeatedly cycles back to the metal interface to cause more
corrosion; the main factors affecting the rate of such corrosion,
besides the presence of chloride, are ambient conditions such as
humidity, surface moisture, and presence of other ionic species. In
conservation we're interested not only in the gross visible effects
of applying salt or acid to promote rusting, but also in effects on
underlying structure and long term stability which may be
undetectable at first. Conservators prefer to err on the side of
caution, although I definitely notice that in the care and
restoration of outdoor sculpture, even otherwise thoughtful
conservators often give short term results priority over
craftsmanship and over long term planning.

If there is more than anecdotal evidence to support your comments, I
will be very glad to see it. A very interesting study I'm in no
position to conduct, might test your hypothesis about chloride
contamination's impact or lack thereof on the development and
protectiveness of weathering steel's patina. I guess the study would
have to employ some of the instrumental methods you find
untrustworthy, since they are among the tools available to
investigate the nature of materials at the scale of interest. They
are some of the methods normally used in studying surfaces,
corrosion products and patinas. It would be instructive to see an
explanation of how the chloride is transported away from the steel
or is otherwise rendered harmless. Although it would simplify
matters tremendously, it would also be very remarkable indeed if
weathering steel proved one of the few instances of metal surface to
which a small amount of chloride contamination such as supplied by
soaking with salt or acid solution was not detrimental. Until this
can be proven, I'm afraid that even from an expert witness it just
isn't convincing, and I cannot use it in the conservation of art.

John Scott
New York Conservation Center

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                  Conservation DistList Instance 12:12
                   Distributed: Friday, July 24, 1998
                       Message Id: cdl-12-12-006
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