pert treatment and a splendid surface finish.

In conclusion, then, the points to be remembered in determining the
origin of corundum gems are four in number.

1. Expect to find natural defects, such as "silk" or cloudy patches, or
_angular_ bubbles in all natural stones.

2. If bubbles are present in artificial material they will be _round_ or
rounding.

3. Artificial material will always have _curving_ parallel striae within
it.

4. The _surface finish_ of artificial material is seldom or never equal
to that of natural material.

It ought not to be necessary to add that material from either source may
be cut to any shape, and that artificial rubies may be seen in most
Oriental garb, hence all specimens should have applied to them the above
tests regardless of the seeming antiquity of their cut or of their
alleged pedigree.

LESSON XVI

HOW TO TEST AN "UNKNOWN" GEM

Having now considered separately the principal physical properties by
means of which one can identify a precious stone, let us attempt to give
as good an idea as the printed page can convey of how one should go
about determining to what species a gem belongs.

SIGNS OF WEAR IN AN EMERALD. To make the matter more concrete, and
therefore more interesting, let us consider a real case, the most recent
problem, in fact, that the author has had to solve. A lady of some
wealth had purchased, for a large sum, a green stone which purported to
be an emerald. After a few years of wear as a ring stone she noticed one
day that the stone had dulled around the edges of its table, and
thinking that that ought not to be the case with a real emerald, she
appealed to a dealer in diamonds to know if her stone was a real
emerald. The diamond merchant told her frankly that, while he was
competent in all matters pertaining to diamonds, he could not be sure of
himself regarding colored stones, and advised the lady to see the
author.

The matter being thus introduced, the lady was at once informed that
even a real emerald might show signs of wear after a few years of the
hard use that comes to a ring stone.

While emerald has, as we saw in the lesson on hardness, a degree of
hardness rated as nearly 8 (7-1/2 in the table), it is nevertheless a
rather brittle material and the long series of tiny blows that a ring
stone is bound to meet with will cause minute yielding along the exposed
edges and corners of the top facets. This being announced, the first
step