Encyclopaedia Britannica > Volume 8, DIA-England

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DIAMOND.
Diamond, diamond was inflammable. In 1673 Boyle discovered that
when it was exposed to a great heat it was dissipated into
acrid vapour. In 1691, the experiments of Boyle were con¬
firmed by those of Cosmo III. Grand Duke of Tuscany,
with his celebrated burning glass. About the same time,
but whether before or not is uncertain, Sir Isaac Newton
was led, from the great refractive power of the diamond,
to pronounce it “ an unctuous substance coagulated.” La¬
voisier proved it to be composed of carbon, by throwing
the sun’s rays concentrated by a powerful lens upon a dia¬
mond inclosed in a vessel with oxygen gas ; when the dia¬
mond and the oxygen disappeared, and carbonic acid was
generated. Sir George Mackenzie repeated the experi¬
ments of Boyle in 1800; and, finally, when Sir Humphry
Davy visited Florence in 1814, the experiment of the grand
duke was performed again with the same lens ; and mine¬
ralogists no longer hesitated to place the gem amongst
inflammable bodies.
According to Ellicot, the specific gravity of Brazil dia¬
monds is 3’513, and of India diamonds 3‘519. The former
is the mean of four, the latter of ten experiments.
Diamond cutting was little understood till 1476, when
an artist of the name of Berghen, residing at Bruges, in¬
troduced the practice of using diamond powder for form¬
ing and polishing the facets. Holland, in consequence,
long maintained a monopoly of this trade; and to this
day the smaller diamonds are almost entirely manufactured
for the European market, at Amsterdam. The Pitt dia¬
mond was, however, cut and polished in London, as most of
the larger sized stones continue to be. It is a very laborious
and tedious operation. The grinding into the required
form is entirely done by the hand. Two stones are ce¬
mented to the ends of tool handles, and rubbed with a
powerful pressure against each other, a leaden model
being first taken of the rough stone intended to be cut.
The faces are thus determined. The two stones are then
rubbed together over a little metal box haying a double
bottom, the upper one being loose and perforated with
small holes, through which the diamond dust passes, and
is carefully preserved. The desired form being thus ob¬
tained, the dust is afterwards used in polishing the faces
of the diamond, mixed up with sweet oil, on a common
lapidary’s wheel, and the brilliancy of the gem brought
out. The period of constant work required to reduce a
stone of between twenty-four and thirty carats to a regular
form will extend to at least seven or eight months constant
work. The Pitt diamond was said to occupy two years.
From the outline in Plate CCII. fig. 1, there was a great
deal of extraneous matter to reduce, and that space of time
may very likely have been required. When the mass to be
removed is of such a size as to render it of importance to
keep it entire, the piece is cut off by means of a steel
wire, extended on a bow of cane or whalebone, anointed
with diamond powder. This process is very commonly
adopted in India. The diamond is sometimes also split
by means of a chisel under a sharp stroke of a hammer;
but this means requires great firmness of mind and dex¬
terity of hand, for a valuable stone is sometimes destroyed
by an unlucky blow.
The forms into which the diamond is cut are the bril¬
liant, the rose, and the table. The first is composed of a
principal face, which is called the table, surrounded by a
fringe composed of a number of facets, which is all that
is visible above the bezil when set. The proportion for
the depth should be half the breadth of the stone, ter¬
minated with a small face, parallel to the table, and con¬
nected with the surface by elongated facets. As the oc¬
tahedron is the most common natural form of the stone,
and the brilliant cut being by far the most advantageous in
point of effect, and the most economical form that can be
adopted, it is hence preferred. The others are suggested Diamond,
by the shape of the mass. v—
The rose is entirely covered with facets on the sur¬
face, and is flat below. The table form is adopted in
consequence of the shape of the mass, whether crystal or
fragment, and produces the least effect. It is principally
used in India, where the native jewellers cleave stones into
plates, having often a large surface with little proportioned
weight or brilliancy, except at the edges, which are orna¬
mented by being cut into facets. The great diamond of
the Mogul emperor, called Derriah Noor, is of this descrip¬
tion ; that called Koh-e-noor is rose-cut.
Much of the value of diamonds depends on the cutting of
the stone. A late celebrated philosopher, who required a
piece of diamond for philosophical purposes, found a large
mass in the hands of a jeweller. It was of an awkward
form, and presented a flaw which very greatly deteriorated
its value, as, in consequence of the refraction and reflec¬
tion which took place within the mass, the flaw seemed to
occupy nearly the whole of the interior. The gentleman,
however, was not afraid. He paid a large sum for the stone,
directed the workman in cutting it, amputated the piece
he wanted, separating the flaw, and sold the remainder
back to the jeweller, after being properly cut and polished,
for double the price he paid for it.
Hopes were recently excited, that a new diamond
district had been discovered in Siberia by the celebra¬
ted traveller Humboldt. He thought he had met with ap¬
pearances in a territory belonging to Count Demidoff,
analogous to that of Minas Geraes, and recommended a
search for the gem. But as two years have since elapsed
without any confirmation of this suggestion, the old locali¬
ties of Asia and Brazil are likely to remain without com¬
petition.
Explanation of the Plate, No. CCII.—The three figures
at the top, No. 1, 2, 3, are representations of the Regent
or Pitt diamond, the Great Mogul, and the Grand Duke,
of the full size and form. No. 4 presents the brilliant cut,
looked at perpendicularly. No. 5, the same sidewise.
No. 6 and 7 also represent the brilliant before it undergoes
the process of re-cutting. No. 8 and 9 are the vertical and
lateral appearances of the rose-cut diamond; and No. 10
and 11, that of the table-cut. The scale No. 12 exhibits
the sizes of the set diamond within the hezil, together with
the depth of the stone, and the number of carats a dia¬
mond of that size is likely to weigh. This estimate can
only be an approximation to the exact weight; but the
weight of a set stone may thus be very nearly ascertained.
No. 13 is the figure of the octahedral diamond seen perpen¬
dicularly, with the table traced where the stone should be
cut; and No. 14 is the same crystal seen laterally, with
the table and the opposite face also traced. By these
figures it will be seen how much more advantageous it
is to adopt the brilliant form than any other.
Diamonds have been imitated with great success by the
French artists. To this composition, to which they give the
name of strass, they not only communicate the adamantine
lustre of the zircon, but succeed in giving it such a simi¬
litude to the real stone in all respects, hardness excepted,
that it is nearly impossible for unpractised eyes to detect
the difference. Recently quartz has been used with great
effect to form the faces of factitious stones.
Diamond used by Glaziers, is an instrument made of
steel or iron, into the point of which a diamond is intro¬
duced and fixed by solder. Care must be taken to place
the gem so that, by applying the instrument in a parti¬
cular position, the angle of the crystal will come in con¬
tact with the glass.
Diamond, in Heraldry, a term used for expressing the
black colour in the achievements of peerage.