|
152
|
PRECIOUS STONES,
|
||
|
|
|||
|
A
cold method consisted in soaking the crystal in a solution of the
coloured resins in turpentine or alcohol ; how staining occurs in this
case is not clear, as ordinary Bock Crystal will not absorb colour ;
still, the Indians seem to have had some secret method of uniformly staining
Quartz. More simple methods were to coat the lower part of the cut
stone with some coloured varnish, and then mount it in a closed
setting. The clear colourless varieties were nearly always set-with
foil at the back.
The
sub-variety known as Iris or Rainbow Quartz, is ordinary Rock Crystal
containing fine flaws, into which air has penetrated as a very thin
film, giving rise to the optical effect of colour as seen in Newton's
rings and in thin soap bubbles. The flaws may be present when found, or
they may be induced by a blow or by cooling suddenly after heating. It
is cut with a low curved surface kept as close to the flaw as possible.
Iridescent
Quartz is Rock Crystal with a thin film of some mineral on the surface
of the crystals ; this film often consists of Limonite or other oxide.
If used for ornamental purposes it must be kept in its natural state,
as the beautiful colour is only a surface effect. Very fine colours are
seen on some of the Quartz from the Caldew in Cumberland.
2.
The variety known as Asteriated or Star Quartz, shows a six-rayed
star when cut normal to the vertical axis, similar to the Asteriated
Sapphire.
3. Amethyst, Quartz of a violet colour.
Although the name is usually derived from a and ìßèí, that is " without wine," King suggests it is more likely that the Greeks adopted an Oriental name, and derived their
|
|||
|
|
|||