Noxon

Henry Grunder called me about this problem.  He needs to polish
copper engraving  plates once used to produce map engravings.   Pure
copper is a relatively soft and ductile metal, so the erosion of the
surface as well as potential polish residue problems in the fine
engraving are concerns.  I recommended that Henry try the precipated
chalk first before going on to more abrasive polishes or those that
have more aggessive chemicals.  The commercial polishes in wadding
are not my favorite--the cloth can catch on sharp edges and the
internices of detail and the abrasives are too aggressive for fine
metal surfaces and soft metals.

Also, I would never recommend lacquering or coating a metal surface
unless all polish residues and chemical residues are removed
(including fingerprints!).  To coat over a less than pristine
surface is to invite a more aggressive and localized  corrosion
problem (under the film) than if you had left the piece cleaned but
in an uncoated state.  You also need a good deal of experience in
applying coatings to metal surfaces to ensure thorough surface
coverage.  You just don't slap the coating on and assume that all is
well.

The recent article on silver "whisker" and filliform corrosion which
was published in the last Studies in Conservation  (Catherine Sease
is one of the co-authors) is an excellent example of what can happen
to coated metal objects if a less-than-thorough coatings protocol is
followed. Cheers,

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

                                  ***
                 Conservation DistList Instance 10:101
                  Distributed: Thursday, May 15, 1997
                       Message Id: cdl-10-101-003
                                  ***