Pewter plates

One of the Hurricane Sandy projects I am working on is a collection
of 18th century local archaeological items--clay pipes, ceramic
sherds, a couple of leather shoes, etc.  The worst-hit is the
metals.  My current problem is with two plates that were thought to
be pewter. They are somewhat squashed, presumably not from Sandy.
They arrived with a marblized-looking surface and several colors of
beige splotches, presumably remnants of the slime and dirt in the
floodwater.  Removal of the top layer leaves a surface that looks
like soot--matte black. Under that, mild abrasion with whiting
reveals a copper-colored--or iron rust-colored--metallic surface.

Since pewter plates can have a maximum of about 1% copper, I don't
understand what I am looking at.  Could the tin be depleted either
from the earlier burial or acidic/salty storm water?  Considering
all the pewter plates that turn up from digs but still look like
pewter, I'm stumped.  Any insights would be very much appreciated.

Barbara Appelbaum
Appelbaum and Himmelstein
444 Central Park West
New York, NY  10025
212-666-4630
Fax: 212-316-1039


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                  Conservation DistList Instance 26:32
                 Distributed: Saturday, January 5, 2013
                       Message Id: cdl-26-32-013
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