Note 16 — Chapter IX · OUR SHELL-FISH FISHERIES.

The following information as to the colour and structure of the pearl may interest the general reader:—

Sir Robert Reading, in a letter to the Royal Society dated October 13, 1688, in speaking of Irish pearls, states that pearls, if once dark, will never clear upon any alteration in the health or age of the mussel. This Mr. Unger stoutly contradicts; he shows by many specimens that some of the finest Scotch pearls are perfectly dark inside. The theory put forth by Sir Everard Home, that the peculiar lustre so much valued in the pearl arises from the centre, is thereby upset. There is no doubt Sir David Brewster is correct in his statement on that point in the Edinburgh Encyclopædia. Some writers assert that irregular pearls may be rounded. This of course is erroneous: they are, as everybody knows, formed in layers like an onion, and these layers being cut across would be exposed in such a manner that even the highest polish would not hide them. It is, however, quite possible in many instances to improve a bad-coloured pearl by removing one or more of the coats; and in this way many a pearl of comparatively trifling value has been turned into a gem of rare beauty. The best way to distinguish a real pearl from an imitation one is to take a sharp knife and gently try to scrape it: if imitation the knife will glide over the surface without making any impression, it being glass, and a real pearl will not be injured by a gentle hand. Pieces of shells are, however, extensively used and sold as pearls. They are cut into shapes closely resembling half pearls, and mounted in various ways, so that many professed judges have been deceived. These are easily to be distinguished by their iridescent lustre from the true pearl, which has but one distinct tint.