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Subject: Ebonite


From: Sue Warren <swarren>
Date: Friday, March 23, 2001
Christina Hallden <christina [at] cfvh__kva__se> writes

>I am currently working on an electrical induction coil in a
>collection of historic scientific instruments and I am looking to
>identify the material of the insulation on the outside of the coil.
>I have read that this material could be Ebonite/Vulcanite but most
>references say that this is a stable material resistant to humidity,
>acids, solvents, oxidation etc. which does not seem to have been the
>case here.

We have a great deal of this material in our collection at the
Canada Science and Technology Museum, and much of it exhibits
similar deterioration. The material could be either Bakelite or
Ebonite; and an easy test is to rub it gently to create a small
amount of friction, so that you can smell it and try to detect a
sulphur smell (like that of old tires). This usually indicates that
the material is Ebonite. Another indicator is the presence of
corrosion of copper alloys in contact with ebonite. In our
experience, Ebonite has more of a tendency to turn brown with age
and light exposure, than does Bakelite.

When new, Ebonite was remarkably impervious to chemical attack, but
we have noticed that as it ages, and with exposure to humidity, and
especially light; its surface becomes discoloured and pitted. It
seems to remain unharmed by chemical cleaning, although the
introduction of water based cleaning solutions can lead to further
discolouration. We generally clean the material with mineral
spirits, and buff the surface gently with a clean rag. We do not
attempt to restore the original surface colour or sheen through the
introduction of polishing compounds or consolidants; since
introducing such products into a deteriorating polymer matrix may
have unpredictable results. Where possible, a barrier layer such as
mylar, is placed between the ebonite and any copper alloy fixtures.

Please feel free to contact me if you have any more questions. Good

Sue Warren
National Museum of Science and Technology
2495 Lancaster Road
P.O. Box 9724, Station T
Ottawa, ON K1G 5A3
Fax: 613-991-0827

                  Conservation DistList Instance 14:49
                  Distributed: Friday, March 23, 2001
                       Message Id: cdl-14-49-002
Received on Friday, 23 March, 2001

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