lustrous,
but the material is very thin. It is commonly provided with a suitable
filling or backing of putty or cement to impart solidity, and is used
like a blister pearl. Sometimes two perfectly matched coques de perle are filled and cemented together, giving the appearance of an abnormally large oblong or nearly spherical pearl.
The
color of pearls has no connection with the luster. In general it is the
same as that of the shell in which they are formed. Black pearls are
found in the black shells of Mexico, and pink pearls in the pink-hued Strombus of
the Bahamas. Ceylon pearls are seldom of any other color than white,
and Sharks Bays are almost invariably quite yellow or straw-colored,
while those of Venezuela are commonly yellowish tinged. But from other
localities, pearls simulate every tint of the rainbow, as well as white
and black. The most common, as well as the most desirable ordinarily,
is white, or rather, silvery or moonlight glint,—"la gran Margherita," as
Dante calls it; but yellow, pink, and black are numerous. They may also
be piebald—a portion white and the rest pink or brown or black. Some
years ago there was on the market a large bean-shaped pearl of great
luster, one half of which was white and the other quite black, the
dividing-line being sharply defined in the plane of the greatest
circumference. The pearls from Mexico, the South: Sea islands, and the
American rivers are especially noted for their great variety of
coloration, covering every known tint and shade, and requiring such a
master as Théophile Gautier to do justice to them.
Many
theories have been advanced to explain the coloration of pearls. When
the old idea of dew formation prevailed, it was considered that white
pearls were formed in fair weather, and the dark ones when the weather
was cloudy. It was further considered that the color was influenced by
the depth of the water in which they grew: that in deep water they were
white, but where it was so shallow that the sunlight easily penetrated,
the pearls were more likely to be dark in color. Tavernier curiously
explained that the black pearls of Panama and Mexico owed their color
to the black mud in which the pearl-oysters of those localities lived,
and that Persian Gulf pearls were more inclined to yellow than those of
Ceylon, owing to the greater putrefaction of the flesh before they were
removed therefrom.1 Two centuries ago the color of a pearl
was attributed to that of the central nucleus, and it was concluded
that if the nucleus was dark, the pearl would be of a similar hue.2
This theory has also been upset, for pearls are found white on the
exterior and quite dark within, and also with these conditions reversed.
1 "Tavernier's Travels," London, 1889, ! See "Report of the Royal Society," Oct.
Vol. II, p. 115. See p. 97. 13, 1688.
