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METHODS OF TESTING STONES.
Hardness of gems, decided according to an arbitrary scale
ranging from 1 to 10, is determined in various ways: to a certain
extent by the file; by one gem scratching a lower in the scale; but
professionally by four "points" of varying penetration, manufactured
for mineralogists and jewelers.
Specific gravity, or the weight of gems, not the weight for
trade purposes by karats, but the heaviness as related to others of
its kind, is obtained usually by three out of six tubes, containing
liquid of varying density. For all practical purposes only three are
needed, numbers 4, 5 and 6, but for rare cases there are 1, 2 and 3.
Methylene iodide is put into three portions, more in 4 than 5 and
still less in 6. 4 is left pure ; 5 and 6 have their density proportionally
reduced by adding benzine drop by drop, until the indicators are
in position, one at the top, the other at the bottom. The liquid must
be mixed thoroughly with a glass rod. Then the stone is weighed
both in air and in these heavy fluids, the difference in weight between
the two mediums, after mathematical working out, determin-
ing the specific gravity accurately.
But, if by any chance two stones of the same general appearance
should be of the same weight and hardness, there are still other
tests, the most effective being the dichroscope, an inexpensive little
instrument, in appearance a sort of tiny telescope, which separates
the rays of light and determines whether a stone is monochroic or
or several.
dichroic, that is, with only one color under analysis
The refractometer is another instrument, disclosing the degree
of refraction, or bending of light, not commonly used, except by
mineralogists.
With a little practice, any jeweler, and even his customers, can
learn to make these tests. It should be a congenial task, these delicate
but not very difficult experiments, for the deft hands of women.
That women of intelligence could become authoritative experts on
gems, if so disposed, is practically certain. Above all, women are
far more accurate than men in their sense of color.
The more complicated tests are for troublesome cases, and not
all, as a rule, are necessary. The "points," or even the jeweler's
file, if backed by experience, throw considerable light, while the di-
chroscope, in nine cases out of ten, will settle the question.
Then, the constant handling of gems, aided by the alert mind,
brings its own instruction. The mere look or feel of a stone is be-
trayal to the connoisseur, and when the lens also is applied, the truth
But this as to the better known stones
can be obtained very nearly.
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