oting the difference in the character of the surface luster of the
garnet part and of the glass part. Garnet takes a keener and more
resinous luster than glass. By tipping the doublet so that light is
reflected to the eye from the sloping top surface, one can see at once
where the garnet leaves off and the glass begins. Even through a show
window one can tell a doublet in this way although here it is necessary
to move oneself, instead of the stone, until a proper position is
obtained to get a reflection from the top slope of the doublet.

If the garnet covers the whole top of the imitation then it is not
possible to get so direct a comparison, but even here one can look first
at the top surface and then at the back and thus compare the luster. It
is also well to closely examine with a lens the region of the girdle, to
see if any evidence of the joining of two materials can be seen.
Frequently the lapidary bevels the edge so as to bring the line of
junction between real and false material at the sharp edge of the bevel.
Boiling a doublet in alcohol or chloroform will frequently dissolve the
cement and separate the parts.

The dichroscope also serves to detect the false character of doublets
and paste imitations, as neither shows dichroism. As rubies, emeralds,
sapphires, and in fact most colored stones of value, show distinct
dichroism, this test is a sure one against these imitations.

Triplets and doublets too may be exposed by dipping them _sidewise_ into
oil, thus removing the prismatic refraction almost completely, as the
oil has about the same refractive index as the stone. One can then look
directly through glass and garnet, or other topping material,
separately, and each material then shows its proper color. Thus zones of
color appear in a doublet or triplet when under the oil. A real gem
would appear almost uniform in color under these conditions.

Round gas bubbles can frequently be found in paste, and hence in the
paste part of a doublet. Also, the natural flaws of the real stone are
never found in paste, but may be present in the real stone part of a
doublet or a triplet. Some imitation emeralds on the market, however,
have been made in a way to counterfeit the flaws and faults generally
found in this stone.

ALTERED STONES. In addition to the out and out imitations made of paste,
and the doublets, there are numerous imitations current in the trade
that are made by staining or by otherwise altering the co