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.

Many of the pocket sleeves used for slide storage and coins are
mostly a PVC polyvinyl chloride sheeting. The become a little stiff
over time and sometime brown a little as they age and off gas. I
have seen the corrosion effects of these sleeves on metals
susceptible to chlorides eg.  Bronze Lead silver etc. Also I have
seen photographic slides stored in these pockets suddenly just go
black. Unfortunately there is no reversing the damage on slides and
the damage on coins can also be irreversible if left too long. In
fact I know of one library where the librarian is convinced
predecessors filed blank slides, they have lost a fifth of their
collection so far. But she will not be convinced.

There are a few suppliers of polypropylene or polyethylene sleeves.
However for coins again consider 'Intercept' a corrosion inhibiting
plastic. Depending on the frequency of use of the coin collection
intercept may allow for safe long term storage after they have been
treated. If regular visual use of the coins is required then this
might be an impediment to viewing.

Always use cotton gloves when handling coins or nitrile gloves Latex
gloves contain damaging sulphur. Wrapping them in acid free tissue
is a good start.


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                  Conservation DistList Instance 23:43
                   Distributed: Tuesday, May 4, 2010
                       Message Id: cdl-23-43-003
                                  ***