Storing coins

Susan White <smwhitewhite [at] aim__com> writes

>Does anyone know how to tell if a particular plastic is likely to
>outgas acidic components?  I have a museum client who has been
>housing Greek and Roman bronze coins in "Archival" plastic sleeves,
>similar to photographic slide sleeves; however, the coins are
>starting to bloom with bronze disease and I'm suspicious that the
>plastic may not actually be suitable for holding bronze coins and
>outgassing corrosive reagents. I tried to test the plastic using a
>pH pen designed for testing paper, but the results were ambiguous.

Try testing the plastic sleeves using the Oddy Test method. A burn
test may indicate if the material is PVC if a green flame is
observed. Some plasticizers will react with copper to form
verdigris, which can look like bronze disease.

There is also the possibility that coins were already contaminated
with corrosives before they were placed into the sleeves, and by
placing them in the sleeves, an unfavourable microclimate has been
created.

George Bailey
Senior Objects Conservator
Australian War Memorial
GPO Box 345 Canberra ACT 2601
Australia
+61 2 6243 4437
Fax: +61 2 6241 7998


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                  Conservation DistList Instance 23:43
                   Distributed: Tuesday, May 4, 2010
                       Message Id: cdl-23-43-006
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