A treatise on gems, in reference to their pratical and scientific value: a useful guide for the jeweller, amateur, artist, lapidary, mineralogist, and chemist

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Printed by A. Hanford, 1838 - Nature - 162 pages
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Page 32 - ... so that the figures of the impression made in the earth may be nicely and perfectly expressed upon the glass. The yellowish tripoli has been found best adapted for this purpose.
Page 164 - Each diver carries down with him a large net in the manner of a sack, tied to his neck by a long cord, the other end of which is fastened to the side of the bark. This net is to hold the oysters gathered from the rock, and the cord is to pull up the diver when his bag is full, or when he wants air.
Page 36 - First, to divide the natural surface of the stone in a symmetrical manner, by means of a number of highlypolished polygonal planes, and thus to bring out to the best advantage the wonderful refulgence of this beautiful gem ; and, secondly, by cutting out such flaws as may happen to be near the surface, to remove those blemishes that materially detract from its beauty, and consequently from its value. " The removal of flaws is a matter of great importance : for, owing to the form in which the diamond...
Page 158 - ... rock ; and their colors are very various, though more usually white or gray. By these mixtures porphyries are produced, rivalling in beauty the best antique porphyry. This rock is polished with so great difficulty, that it is rarely used in our country, either for ornamental or useful purposes. But it would be strange if an increase of wealth and refinement should not create some demand for so elegant and enduring a rock. Whenever this shall happen, the vicinity of Boston will furnish every variety...
Page 66 - The most perfect and beautiful diamond hitherto found is probably that brought from India by an English gentleman of the name of Pitt, who sold it to the Duke of Orleans, by whom it was placed among the crown jewels of France. This jewel weighs rather more than 136 carats, and was sold for the sum of J
Page 68 - ... and Maltese crosses equally rich. In the front of the Maltese cross which is in front of the crown is the enormous heart-shaped ruby, once worn by the chivalrous Edward the Black Prince, but now destined to adorn the head of a virgin queen.
Page 83 - Indies, is said to have given to the king of England, among other presents, an Emerald of the size of a hen's egg. The treasury of Vienna is said to contain an Emerald of two thousand two hundred and five carats, valued at three hundred thousand crowns. The most magnificent specimen of Emerald was presented to the cathedral of Loretto, by one of the Spanish kings. It consists of a mass of white quartz, thickly implanted with Emeralds, more than an inch in diameter.
Page 38 - ... the Diamond is placed on the plate, the pincers resting on their legs on the wooden bench or table that supports the plate, and pressing at the same time against an upright iron peg ; the broad part of the pincers between the legs and the Diamond, is then loaded with weights, both to steady the machine, and to increase the pressure of the Diamond against the skive. Matters being thus adjusted, a little oil and Diamond powder is dropped on the plate, it is set in motion at the rate of about...
Page 40 - This cut displays to greatest advantage the lustre of the diamond : it may be considered as obtained by two truncated pyramids, united together by one common base, the upper pyramid being much more deeply truncated than the lower. It is formed — a, of the crown, or that part...
Page 95 - Emeralds are cut on a copper wheel with emery, and polished on ' a tin wheel with rotten-stone. " In a good gem," says Mr Emanuel, " the surface must be perfectly straight and smooth, so as to cast no darkening shadow on any of its particles.

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