Oddy tests

Will Jeffers <wjeffers [at] mfa__org> writes

>... is there any evidence of the
>Oddy test producing false negative results?

A few possible explanations spring to mind that could explain a
material passing the test and then subsequently causing problems.

The tests are generally carried out with the metal coupon separated
from the test material to detect airborne gases.  Several species
such as some chlorides are not volatile and will not fail the test
in its normal configuration, but if the material is placed in direct
contact with artefacts will cause corrosion. It may be prudent to
modify the tests, if a material is to be used in this way. Fabrics
are very good at absorbing the gases around them and storage
conditions can lead to problems.  A roll of fabric that had been
tested as suitable for use with silver, absorbed sulphide gases from
storage with other fabrics and became unsuitable for use.
Fortunately this was discovered during a subsequent test, before
installation.

There may be some variation in the composition of materials from
batch to batch; manufacturers may change the composition without any
notification and very few materials are quality controlled for
emisions.   If the sample tested was not from the batch used, then
it may have different properties. Photodegradation of materials
could also possibly be a culprit, as the tests are carried out in
the dark.

David Thickett
Conservation Scientist
Department of Conservation
The British Museum
London WC1B 3DG
+44 171 323 8772
Fax: +44 0 171 323 8276

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                  Conservation DistList Instance 12:12
                   Distributed: Friday, July 24, 1998
                       Message Id: cdl-12-12-014
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