ce-portion of paste. In other cases the whole of the
crown is genuine, whilst often both the upper and lower portions are
solid and genuine, the saving being effected by using a paste centre at
the girdle, covered by the mounting. Such a stone as this last mentioned
is often difficult to detect without using severe tests and desperate
means, e.g.:--(a) by its crystalline structure (see Chapter III.);
(b) by the cleavage planes (see Chapter IV.); (c) by the polariscope
(see Chapter V.); (d) by the dichroscope (see Chapter VI.); (e) by
specific gravity (see Chapter VIII.); (f) cutting off the mounting,
and examining the girdle; (g) soaking the stone for a minute or so in
a mixture said to have been originally discovered by M. D. Rothschild,
and composed of hydrofluoric acid and ammonia; this will not answer for
all stones, but is safe to use for the diamond and a few others. Should
the jewel be glass, it will be etched, if not completely destroyed, but
if genuine, no change will be apparent; (h) soaking the diamond for a
few minutes in warm or cold water, in alcohol, in chloroform, or in all
these in turn, when, if a doublet, or triplet, it will tumble to pieces
where joined together by the cement, which will have been dissolved. It
is, however, seldom necessary to test so far, for an examination under
the microscope, even with low power, is usually sufficient to detect in
the glass the air-bubbles which are almost inseparable from
glass-mixtures, though they do not detract from the physical properties
of the glass. The higher powers of the same instrument will almost
always define the junction and the layer or layers of cement, no matter
how delicate a film may have been used. Any one of these tests is
sufficient to isolate a false stone.

Some of the softer genuine stones may be fused together with splinters,
dust, and cuttings of the same stones, and of this product is formed a
larger stone, which, though manufactured, is essentially perfectly real,
possessing exactly the same properties as a naturally formed stone. Many
such stones are obtained as large as an ordinary pin's head, and are
much used commercially for cluster-work in rings, brooches, for
watch-jewels, scarf-pins, and the like, and are capable of being cut and
polished exactly like an original stone. This is a means of using up to
great advantage the lapidary's dust, and though these products are real
stones, perhaps a little more enriched in colour chemica