As " paste" can be
made so as to have the same specific gravity as the genuine article,
this test alone cannot be relied upon; but very few of the imitations
are so carefully made. The test is very convenient in distinguishing
gems of like color from each other, as oriental ruby, spinel ruby and
red tourmaline, and green tourmaline and emerald.
Thirdly: characteristics depending on light and electricity. It
is not easy to look through a diamond of the first waier, while
imitations readily permit objects to be seen through them. A very
delicate and perfect test of a diamond, distinguishing it from all the
colorless gems, as white topaz, white sapphire and white zircon, but
not from " pastes," is to look through it at a pin-hole in a card. This
requires some dexterity, and the gem should be fixed to a steady
object by a bit of wax at a proper distance. A true diamond will show
but one hole, all the others will show two. As white topaz, when large,
is a magnificent stone, it is. often palmed off for a diamond of great
value; but this test is invariably certain. A true diamond retains its
brilliancy under water.
When
a colored stone is placed in the path of the solar spectrum (the row of
seven colors into which sunlight is separated by a prism), its color
will vary with the portion of the spectrum which falls upon it ; and
two stones of the same color, but of a different nature, will exhibit
different effects. Thus, a paste placed beside a fine colored gem,
betrays its worthlessness. A simpler method of testing stones is to
look at them through a bit of glass, colored red, yellow, blue or
green. Every stone will exhibit, under this test, properties peculiar
to itself, and by which its nature may be recognized. This is also a
severe test for the purity of tint; for if pure and unmixed, the stone
will appear completely black in every other light but its own color.
Milky and turbid stones cannot bear this test.
A
first-class ruby has the color of the blood as it spirts from an
artery. The deeper the hue of the emerald the more it is valued; it
loses none of its brilliancy by artificial light. The pale rose topaz,
the kind most esteemed, is artificially colored by heating it.
If
topaz or tourmaline be gently heated, it becomes electric and will
attract a thread or suspended pith-ball. No imitation will do this. All
real gems when rubbed will attract the pith-ball, and retain the power
a long time; the pastes also become electric, but soon lose their
attraction. Rub a glass tube with a piece of flannel and bring it near
a suspended pith-ball; the latter will be strongly attracted and then
repelled, lmmediatelv rub a genuine diamond and bring it near the
ball, and it will be attracted. A paste diamond thus rubbed would repel
it.
Finally:
the breath remains much longer on the pastes than on real gems. The
former also betray under a magnifying glass small air bubbles. Diamonds
and other first-class stones are always cold to the touch.
Falsi: Pearls.—These
are glass beads coated with a mixture of three ounces'of scales of the
blay or bleak fish, half an ounce of fine glue, one ounce of white wax
and one ounce of pulverized alabaster. Powdered opal is sometimes used;
also the powdered pearl of the oyster and other shells soaked in
vinegar, and made up with gum tragacanth. Artificial pearls are usually
brittle, and do not weigh more than two-thirds as much as the genuine.
False Corals.—These
are made of resin and Vermillion ; or of marble powder made into a
paste with varnish or soluble glass and a little isinglass, colored by
Chinese vermilion and then moulded. They are used for setting in cheap
jewelry. The knife shows it to be too soft to be genuine.
Artificial Gold.—The
following oroid or imitation gold is sometimes sold for the genuine
article which it closely resembles. Pure copper ioo parts by weight, is
melted in a crucible, and then 6 parts of magnesia, 36 of sal-ammoniac,
1-8 of quicklime and o' of tartar are added separately and gradually in
the form of powder. The whole is then stirred for about half an hour,
and 17 parts of zinc or tin in small grains are thrown in and
thoroughly mixed. The crucible is now covered and the mixture kept
melted for half an hour longer, when it is skimmed and poured out.
