Cleaning turquoise

Eileen Procter <eileen.procter<-a t->awm< . >gov< . >au> writes

>I have a piece of turquoise mounted in sterling silver. It has been
>previously worn and now the turquoise has yellowed but the silver
>has not tarnished.  The silver is not coated.
>[I] would like to know if the
>discolouration can be removed and if so, what would be the best way
>to go about it.

Turquoise is a copper and aluminum phosphate mineral that is subject
to fading by light.  For a discussion of the mechanism see Kurt
Nassau's chapter "Conserving light sensitive minerals and gems" in
The Care and Conservation of Geological Materials published by
Butterworth-Heinemann in 1992.  Note also that low grade turquoise is
sometimes dyed to enhance its color and deterioration of a dye stuff
may be part of the problem. There is also the possibility that the
polishing process was short cut by the addition of a natural or
synthetic varnish or coating and that the coating has yellowed. Good
luck,

Kory Berrett
Berrett Conservation Studio
3054 Reisler Road
Oxford, PA 19363
610-932-2425

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                  Conservation DistList Instance 11:57
                Distributed: Tuesday, December 30, 1997
                       Message Id: cdl-11-57-002
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