Rock Crystal
Q: I deal in vintage costume jewelry. I just picked up three crystal necklaces
at a flea market. I suspect that one of them might be rock crystal
(quartz?) instead of leaded glass. I suspect this because it is noticibly
colder to the touch than the other necklaces. Am I on the wrong track, or
is this an indication of composition?
Also, I just sold a necklace on ebay which I thought was orange crystal.
The buyer, who is a jewelry dealer of some sort, emailed me to thank me, and
told me the necklace was actually real cut citrine. Also, I sometimes get
sterling jewelry set with stones that I suspect to be semi-precious.
Short of a class at the gemnology isntitute (which I have been considering,
btw), is there any simple way to tell semi precious stones from glass?
A:Actually, no. An RI is the most informative test to determing exactly which type
of material OTHER than glass you might have, but a refractive index measurement
won't always tell you if you have glass, since glass can have almost any
refractive index. Of course, if you see a double refractive RI measurement,
then of course, it can't be glass. But a polariscope is simpler to use for this
purpose, and you can make a home brew version of one for a few dollars, while a
refractometer is harder to use, and will cost a bunch of money. And the
appearance of glass or plastic under a polariscope is different, usually, from
that of other single refractive materials.
Frankly, with just a little practice, all you really need, most of the time, is
just a good loupe, to seperate glass from other materials in costume quality
materials.