Silver foil for Oddy tests

The 'standard' silver was chosen primarily because it was readily
available in the UK, quality controlled for composition and easy to
work with.  I agree with Will Jeffers's comments regarding thickness
and purity, at least to a level of say 99%.

Debasing the silver (with copper) will make it more reactive towards
sulphur gases.  This reactivity seems to peak at around 7.5% copper,
Sterling silver.  There may be an argument that we should be using
this sterling silver for the tests, after all many silver artefacts
are debased to some extent.  My feeling is that the test is actually
quite sensitive as it is and there is no need to improve this.  One
also needs to bear in mind that the background concentration of
sulphur gases  in the air will tarnish silver in showcases even if
all internal sources have been removed by testing.  Air-conditioning
or positive pressure systems with absorbents could overcome this.

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

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                  Conservation DistList Instance 12:35
                 Distributed: Thursday, October 8, 1998
                       Message Id: cdl-12-35-005
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