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CUTTING
Precious stones are cut and polished to develop the beauties which are latent in them.
Uncut,
the diamond is not beautiful. In the rough, at its best as an
octahedral crystal, it does not equal in appearance a piece of cut
glass; generally it is an irregular, rough, luminous gray pebble. But
it has inherent qualities which can be made beautiful. It will take a
high polish; it has the power to reflect and disperse light falling
upon it to an extraordinary degree, and to strongly refract and reflect
the rays which enter its transparent body.
By
cutting and polishing, the natural adamantine lustre, or surface power
of reflection, is utilized to throw back as much as possible upon the
eye the light-rays as they impinge upon the facets arranged to
intercept and disperse them.
But
as all the light cannot be held by the surface, advantage is taken of
its reflective and refractive powers to hold and concentrate by the
angles and arrangement of the back facets the light which enters the
body of the stone. Knowing the exact angle to which rays of light are
bent on entering, and the angle at which light endeavoring to pass from
a denser medium into the air, as from a diamond, is totally reflected,
it has been found possible to so form it and arrange its back facets as
to catch the fugitive rays in their effort to pass through, and, by
driving them back and forth among the adamantine walls, round them up
within the interior and finally return them in brilliant flash-lights
through the face of the stone, to the delighted eye of the beholder.
The primitive method of cutting diamonds was simply " bruting," or by rubbing one crystal against another, to grind
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