The brilliant hues of mother of pearl do not depend so much upon the nature of the substance as on its structure. Its surface is covered by minute corrugations or furrows, which give a chromatic appearance to the reflected light. Sir David Brewster was the first to show that this substance is capable of imparting its iridescent appearance to fusible metal or fine black wax.
Mother of pearl is cut and wrought with nearly similar tools to those used for ivory, but its treatment, owing to its more fragile nature and delicate structure, requires considerably greater care. It is polished with colcothar or putty powder.
The numerous applications of mother of pearl, for buttons and knife-handles, boxes, inlaying work, &c., are well known.
PEARL′ASH. This is prepared by calcining crude potashes on a reverberatory hearth, dissolving the calcined mass in water, and, after repose, decanting the clear solution, and evaporating it to dryness in flat iron pans, the product being constantly stirred towards the end to reduce it to a semi-granular state. Although purer, its richness in absolute alkali is less than that of the potashes from which it is prepared, being only from 47% to 51%. This exists almost entirely under the form of carbonate. The commercial value of this substance is determined by the ordinary processes of Alkalimetry.
PEARL BARLEY. See Barley.
PEARL FLAVOUR. See Essence.
PEARL WHITE. This is a subchloride of bismuth; but the name is now commonly applied to trisnitrate of bismuth, which is sold for it.
PEARLS (Rose). Syn. Rose beads. The petals of red roses beaten in an iron mortar for some hours, until they form a smooth, black paste, then rolled into beads and dried. Hard; very fragrant; take a fine polish.
Pearls, to Polish. Take very finely pulverised rotten stone, and make it into a thick paste
by adding olive oil; then add sulphuric acid, a sufficient quantity to make into a thin paste.