A Treatise on Diamonds, and Precious Stones: Including Their History--Natural and Commercial. to Which Is Added, Some Account of the Best Methods of Cutting and Polishing Them
A Treatise on Diamonds, and Precious Stones: Including Their History--Natural and Commercial. to Which Is Added, Some Account of the Best Methods of Cutting and Polishing Them
This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1813 Excerpt: ...in which the summits of the primitive rhomboid are replaced by secondary planes that present a varying chatoyant lustre. If these crystals are cut en cabochon, or in the form of an ellipse, taking care that the summit of the ellipse shall be situated exactly over the point corresponding with the summit of the rhomboid, ...
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This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1813 Excerpt: ...in which the summits of the primitive rhomboid are replaced by secondary planes that present a varying chatoyant lustre. If these crystals are cut en cabochon, or in the form of an ellipse, taking care that the summit of the ellipse shall be situated exactly over the point corresponding with the summit of the rhomboid, there will be produced the appearance of a star, with six rays from which, when held in the sunshine, a bright yellowish white light streams forth in beautiful contrast to the rich purplish blue of the other part of the stone. The largest Sapphire that I have ever seen, weighs about 310 carats, (two ounces) and among the crown jewels of France, is a fine rhomboidal crystal of the same, of the weight of 166 carats. The best Sapphires come from Ava and Pegu, where they accompany the Ruby. They are also frequent in the sands of certain streams in the island of Ceylon, but these latter are usually of a pale colour, and are also deformed by streaks and blotches of an inky hue. In France, they have been met with in the sand of the brook Expailly, in Forez, but of so inferior a quality, that the jeweller has never been able to make any use of them. Besides the Ruby and Sapphire, or the red and blue varieties of the Oriental gem, (called by Hauy, Telesia, and by Bournon and Greville, perfect Corundum, ) there are some other varieties, depending merely on colour, that require a short notice. Sometimes this gem is met with of a yellow colour, and more or less mingled with red; in this state, it is called Oriental Topaz; its value is inferior to that either of Ruby or Sapphire; it is, however, a very beautiful substance. The most esteemed colour is a bright jonquil yellow, and next to that, the pure lemon yellow. The rich reddish brown variety, is often ..
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