Not pastes only but clear crystals have long been palmed off on the unwary for diamonds. Perhaps the best-known of these were crystals of quartz found in the Clifton limestone near Bristol, which went by the name of Bristol diamonds. They are alluded to as worn in the ears by the fop described in Lenton's _Young Gallant's Whirligigg_ (1629). Quartz crystals found in the tin mines of Cornwall, and similar stones from the neighbourhood of Harrogate, still known respectively as Cornish and Harrogate diamonds, were also much employed for jewellery from the sixteenth century. Transparent stones from various parts of the Continent are given the names of the localities in which they are found. In France, rock crystal, cut in rose or brilliant form, went generally by the name of _Pierre d' Alençon_ or _Caillou du Rhin_. Of the transparent glass paste termed Stras or Strass we have already spoken. Though an imitation, the paste of eighteenth-century jewellery does not necessarily belong to the category of frauds and counterfeits, since it possesses a certain originality of its own, and does not appear to have been generally worn with intent to deceive. False or mock pearls on the other hand seem in some way to be rather more associated with deception, though they also can be made to serve for decorative purposes entirely apart from any such intent. To reproduce the lustre or "orient" characteristic of oriental pearls, use is made in the fabrication of imitations of a pearly essence known as _essence d'orient_, obtained from the silvery scales on the underside of a fish called the bleak. Beads of blown glass slightly opalescent and treated with acid to produce an iridescent surface are coated internally with a film of the essence, and wax is then introduced to give the bead the desired weight. Other mock pearls are made up of a vitreous composition formed largely of the pearl essence. Their surface when burnished presents a fine lustre. These are generally termed Venetian pearls. Roman pearls are formed of external coatings produced by frequent dippings into a solution made of the pearliest parts of the oyster.