Metal spraying

I have a basic reaction to Ton Cremers posting on the protection of
outdoor metal sculpture via the application of sprayed metallic
droplets.

In many applications, such as the one sited--for the protection of
nuclear waste containment systems, and for artistic purposes in
creating more durable new works of art, this idea sounds exciting.

However, in terms of the conservation of ancient, historic, and
artistic works this process could well violate the integrity of the
piece (aka. "refinishing"), and it is most likely a non-reversible
process.

All metal coating, cladding, and plating processes demand a
completely new, fresh metal substrate to work.  For newly created
works of an industrial or artistic nature this might be fine.
However, for an ancient, historic, or artistic work where we must
have an interest in preserving patinas, previous gilding or
coatings, and even some corrosion products, to mechanically strip or
chemically pickle a surface back to bare, fresh metal would be,
in-and-of-itself an act of significant destruction.

One might very well protect a bronze from the external environmental
forces of humidity, acid rain, et. al, but it is a well documented
phenomenon that copper alloys are prone to suffer from an internal
corrosion process of dealloying when other metallic elements or
complexing agents are in intimate contact with the substrate.  So,
do we clad a bronze sculpture in titanium, stainless steel, or back
in bronze?

Many of us whom conserve gilt, plated, and coated metals have seen
the serious effects that can happen when a protective coating is
scratched, abraded, or worn away even in small, discrete areas.  The
subsequent electrochemical corrosion can be quite severe.  We all
know that such metallic coatings do not remain coherent and
continuous without year-after-year of maintenance - hence the
multiple layers of gilding which are often encountered on outdoor
bronzes.

I would much prefer to remove and renew a wax or resin coating then
to have to face the nightmare of removing or renewing an applied
metallic one. Cheers,

David Harvey
Associate Conservator,
Metals & Arms
The Colonial Williamsburg Foundation
P.O. Box 1776
Williamsburg, Virginia  23187-1776  USA
757-220-7039

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                  Conservation DistList Instance 11:68
                 Distributed: Monday, February 9, 1998
                       Message Id: cdl-11-68-002
                                  ***