Coins

Blake Walter <bwalter [at] tiu__edu> writes

>Each coin is mounted inside of a 4 x 2 x 1/2 inc block of what
>appears to me to be solid acrylic.  If I look at one of the blocks
>edgewise, I can see a thin line running through the middle that
>makes it look like each coin was laid flat on a thin block of
>acrylic along with a translucent label identifying the coin, and
>then a layer of acrylic was poured on top, sealing in the coin and
>its label.  The gold and silver coins appear to my untrained eye to
>still be in good condition, but the bronze coins show a lot of
>corrosion.  (One coin, identified as a lepton from 37-44 AD, has
>discolored the acrylic around it with a purple haze.)
>
>I have volunteered to do the initial legwork in figuring out what it
>would take to restore the collection.  Specifically, I am wondering
>if it is even possible to undo the damage that has been done--can
>the coins be extracted from the acrylic without being destroyed? And
>who would do this kind of work?

We have been investigating this problem for several years now with
sports cards in plastic.  We found that many plastics formers who
specialize in plexi box making, to order forming and shaping, etc.
have a tool called a Thermosheer.  This devise allows one to avoid
the use of a lot of solvent and shave down the block to within a
1/16 or at times, a 32nd of an inch.  In this state the object can
be approached with solvents to reduce the last layers.  However,
while it appears to have been theoretically required that objects be
coated in a separating film prior to immersion in the plastic resin
block, this seldom occurred in our experience.  Therefore, be
prepared to go right from the resin block to the object.

Niccolo Caldararo
Director and Chief Conservator
Conservation Art Service




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                  Conservation DistList Instance 14:53
                   Distributed: Sunday, April 8, 2001
                       Message Id: cdl-14-53-005
                                  ***