cientific emeralds" have proved to be either of paste of
one sort or another, or else triplets having a top and a back of some
inexpensive but hard stone of pale color, and a central slice of deep
green glass, the three pieces being cemented together so skillfully
that the junctions frequently escape any but a very careful examination
with a lens.

ALL SCIENTIFIC STONES ARE CORUNDUM GEMS. Now the fact that all true
scientific stones are corundum gems makes their determination fairly
simple on the following basis: Among the considerable number of corundum
gems of nature, whether ruby or sapphire of various colors, there is
seldom found one that is entirely free from defects. Almost always, even
in what are regarded as fine specimens, one will easily find with a
glass, defects in the crystallization. Moreover these defects are
characteristic of the corundum gems.

The scientific corundum gems, however, never have these specific
defects. Hence the surest and simplest way of distinguishing between the
two kinds of stones is to acquaint oneself with the typical defects of
natural corundum gems, and then to look for such defects in any specimen
of ruby or sapphire that is in question.

While a description of some of the most common of the typical defects of
rubies and sapphires is to follow, the jeweler, who may not yet be
familiar with them by actual experience, owes it to himself and to his
customers to acquaint himself at first hand with the natural defects of
such material, which he is always in a position to do through the
courtesy of representatives of houses dealing in precious stones, if he
himself does not carry such material in stock.

TYPICAL DEFECTS OF NATURAL CORUNDUM GEMS. Perhaps the most common of the
defects of natural corundum gems is the peculiar appearance known as
"silk." This is best seen when a strong light is allowed to stream
through the stone at right angles to the observer's line of sight. Sets
of fine, _straight_, parallel lines will be seen, and these will
frequently meet other sets of similar lines at an angle of 120 degrees
(like the angle at which the sides of a regular hexagon meet) or the
lines may cross each other at that angle or at an angle of 60 degrees
(the supplement of 120 degrees). Such _straight_ parallel lines are
never seen in scientific stones, and their presence may be taken to
indicate positively that the stone having them is a natural stone. In
fine specimens of natural rub