I would also like to add that Emily William's comments are worth noting. As
a conservator of these materials, I never clean the corrosion off copper
alloys with any type of acid. I want to stress the importance of leaving as
much copper corrosion in place until someone with a chemistry background or
analytical equipment can look at the corrosion up close. There are so many
things that it can tell someone. The very discovery of buttons themselves
indicate the loss of some organic material to the burial site, but their
presence also indicates burial facts such as a neutral pH, low transport of
water and oxygen most likely and determined by what type of corrosion, the
presence or absence of salts and ions in the ground. It is very common to
see textile fragments, threads, inlays, hair, food remains and other
organics within the corrosion layers of copper alloys. Coppers and their
compounds are natural biocides, and deter microbial action while in burial,
so it is very common with coppers to find remains within the corroded layer
which can add data to the archaeological record. There have been numerous
studies of this reported in the archaeological literature.
I also want to add that there are so many historical documents from this
time period available, as you said-- these are standard, common buttons of
which you are finding multiples of. Through archaeological reports,
archives, published papers, historical accountings and even artifact
catalogs of our colleagues who have encountered similar sites with similar
buttons, why not look there first to compare your findings and see if there
may be available markings, inscriptions and data to look at before taking
away evidence on the artifacts at hand.
For more information on archaeological conservation of materials you are
finding please visit the Society for Historical Archaeology website,
Conservation FAQs where many of these questions and more have been
addressed.
Lisa Young
President
Alexandria Conservation Services, ltd.
Annandale, VA
703-503-5346/ phone and fax
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-----Original Message-----
From: HISTORICAL ARCHAEOLOGY [mailto:[log in to unmask]] On Behalf Of
Williams, Emily
Sent: Sunday, April 13, 2008 2:24 PM
To: [log in to unmask]
Subject: Corrosion on Brass buttons
While many of the postings mentioned using weak acids to clean the buttons
none of them referred to the need for rinsing afterwards. I would like to
underscore the critical need for rinsing after using any acid. If you don't
the acid is likely to remain on the surface and can be activated by moisture
in the environment causing long term instability and even eradicating the
inscriptions for which you were searching. I would recommend rinsing for
one hour in deionized or distilled water. If you cannot run the water
gently over the piece, make sure to change it several times during the
course of the hour.
Typically we avoid chemically cleaning copper alloys. Chemical cleaning is
hard to control. It can remove important information such as textiles
fragments, stitching fragment, metallic washes, organic coatings and enamels
that could be present on some buttons. Additionally, it can affect
elemental analysis by preferentially removing some components of an alloy.
My recommendation is that before you chemically clean any copper you examine
it under a microscope with both raking light and overhead light. Often
inscriptions can be read in this manner or some judicious and gentle
mechanical cleaning can be used to remove large areas of concretion.
Emily Williams
Conservator of Archaeological Materials
The Colonial Williamsburg Foundation
Department of Conservation--BHW
P.O.Box 1776
Williamsburg, VA 23187-1776
Tel: 757-220-7079
Fax: 757-565-8752
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