It is easy, however, to detect this class of pearls by the lack of pearly lustre on the side that was attached to the shell.
When a pearl is rough and odd-shaped it is called a baroque, and some extremely fantastic shapes are found, especially in fresh-water oysters.
The texture or skin of a fine pearl should be perfectly smooth and free from all spots, indentations, wrinkles, or scratches.
Pure white is the desirable color for a gem pearl, but many others that are slightly tinted with blue, pink, or yellow will pass for gems if they are otherwise perfect.
The transparency or “water” of a pearl, while not existing in fact, is still one of the requisites of a fine pearl; there must be an appearance of transparency, which adds to the beauty of the gem.
To describe the lustre or orient of the pearl, the author can only use the term pearly, as there is no other substance that approaches the brilliancy and color of a pearl, excepting, of course, mother-of-pearl—the nacre in the pearl-oyster.
Without orient or lustre, the pearl of finest form and color has but little value.
Lustre is to the pearl what brilliancy is to the diamond; when the orient is absent there is no life, no beauty.
Pearls are principally supplied by two groups of pearl-oysters or mussels: the marine or meleagrina margaritifera, a round-cornered square shell with very thick sides, measuring six to eight inches in length.
The color of this shell is mostly blackish-green, but it is also sometimes yellowish; the edges of the inner part of the shell are black, but the rest of the interior is the beautiful mother-of-pearl.