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.

>From the description you have given regarding the yellowing of the
turquoise, it sounds to me as if you have a piece that includes
turquoise treated with epoxy resin.  This is a common pre-treatment
of turquoise (especially lower grade material that is too soft to
wear well or even hold together on its own).  As turquoise is a
fairly expensive stone, this pre- treatment has been used extensively
to allow  cheaper stone to be utilized.  In the US Southwest the use
of this material in Native American and Native American inspired
work is common and has been a cause of concern as it has in some
cases been passed off as "real turquoise" when in fact it has been
treated. Untreated turquoise tends to darken and become more green
in color as it ages with use and the accumulation of body oils on
its surface.

I personally know of no way to retreat this material so as to remove
the yellowing.

J. Claire Dean
Dean & Associates Conservation Services
3438 NE 62nd Avenue
Portland, Oregon 97213, USA

                                  ***
                  Conservation DistList Instance 11:57
                Distributed: Tuesday, December 30, 1997
                       Message Id: cdl-11-57-004
                                  ***