356 Glossary
Well. Name given to the dark centre of a diamond cut too thick.
Wesseltons. Third grade cut diamonds.
X-Rays. (Röntgen
Rays.) A recently discovered form of radiant energy that is sent out
when the cathode rays of a Crookes tube strike upon the opposite walls
of the tube or upon any object in the tube; discovered in 1895 at
Würzburg, Germany, by Professor W. C. Röntgen. By means of these rays
it is possible to see and photograph bones, bullets, or other opaque
objects through the fleshy parts of the body. The X-rays are of some
value in testing mineral substances represented as precious stones.
Under X-rays the diamond is transparent ; the glass, or " strass," used
to manufacture imitation diamonds is always opaque under this exposure.
Yellow Ground. The upper diamond-bearing clay of South African mines.
