Hello… I have been lurking… enjoying… learning from this list.
As a neophyte silversmith/jewelry-maker working with semi-precious
stones. I have many questions, many of which have already been
answered on this list. I also appreciate the sources mentioned by
others. My question is this: some of the pre-cut turquoise cabs I
have purchased have backing on them. What is the dark,
composite-looking material made of? If indeed, it strengthens the
material, perhaps I too should use it on the stones I cut… where is
it obtained? How is it applied? Is it the same thing as backing on
opal triplets?
My question is this: some of the pre-cut turquoise cabs I have
purchased have backing on them. What is the dark, composite-looking
material made of?
A thick epoxy or plastic steel. It is used to fill in an uneven
surface, as well as providing some stability to the turquoise which
is very brittle and is easily broken. It is not needed on other
stone, however you will see a black back on some opal doublets which
is a different mater.
Vera, We used a lot of auto body filler for backing of turquoise back
in the turquoise hey day. Backing was applied for two reasons. 1.
We would cut thin nuggets in half and put the rough side in the
backing then cab the top. Thus getting two cabs instead of one. 2.
Thin slices could be made from larger material and many cabs could be
made. Thus increasing the yield of the material. Backing was
applied to make more money and for no other reason. Unusable
material became useable. Today the practice is still followed and
for no good reason. Stabilized rock does not need a backing and most
turquoise is stabilized. It is backed because turquoise sells by the
carat and the backing increases the weight. Natural turquoise cabs
are very expensive and almost unattainable because most turquoise is
stabilized. Turquoise is stabilized to stop the rock from oxidizing
and to make softer turquoise useable.
find soime old broken 78 rpm phongraph record s epoy them to make a
perfect backing after grinding off some of the groves and shellac
LeonK in hot sunny St Louis