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In process of time, as human industry is ingenious in discovering, it was not content with the combination of nitre, but magnet-stone1 began to be added as well; from the impression that it attracts liquefied2 glass as well as iron. In a similar manner, too, brilliant stones of various descriptions came to be added in the melting, and, at last, shells and fossil sand. Some authors tell us, that the glass of India is made of broken crystal, and that, in consequence, there is none that can be compared to it.

In fusing it, light and dry wood is used for fuel, Cyprian copper and nitre being added to the melting, nitre of Ophir3 more particularly. It is melted, like copper, in contiguous furnaces, and a swarthy mass of an unctuous appearance is the result. Of such a penetrating nature is the molten glass, that it will cut to the very bone any part of the body which it may come near, and that, too, before it is even felt. This mass is again subjected to fusion in the furnace, for the purpose of colouring it; after which, the glass is either blown into various forms, turned in a lathe, or engraved4 like silver. Sidon was formerly famous for its glass-houses, for it was this place that first invented5 mirrors.

Such was the ancient method of making glass: but, at the present day, there is found a very white sand for the purpose, at the mouth of the river Volturnus, in Italy. It spreads over an extent of six miles, upon the sea-shore that lies between Cumæ and Liternum, and is prepared for use by pounding it with a pestle and mortar; which done, it is mixed with three parts of nitre, either by weight or measure, and, when fused, is transferred to another furnace. Here it forms a mass of what is called "hammonitrum;" which is again submitted to fusion, and becomes a mass of pure, white, glass. Indeed, at the present day, throughout the Gallic and Spanish provinces even, we find sand subjected to a similar process. In the reign of Tiberius, it is said, a combination was devised which produced a flexible6 glass; but the manufactory of the artist was totally destroyed, we are told, in order to prevent the value of copper, silver, and gold, from becoming depreciated.7 This story, however, was, for a long time, more widely spread than well authentieated. But be it as it may, it is of little consequence; for, in the time of the Emperor Nero, there was a process discovered, by which two small glass cups were made, of the kind called "petroti,"8 the price of which was no less than six thousand sesterces!

1 "Magnes lapis." See B. xxxiv. c. 42, and Chapter 25 of this Book. Beckmann is of opinion that an ore of Manganese is meant, a substance which has a resemblance to the magnet, and is of the greatest utility in making glass. Hist. Inv. Vol. II. p. 237.

2 This appears to be the meaning of "Quoniam in se liquorem vitri quoque ut ferrum trahere creditur."

3 In the description given by Isidorus in the "Origines," which in other respects is similar, these words are omitted, and it is possible that they are a gloss by some one who was better acquainted with the Old Testament than with Pliny. On the other hand, as Sillig remarks, the Phœnicians may, at an early period, have imported into Greece a substance which they called "nitre of Ophir."

4 See Beckmann, Hist. Inv. Vol. II. p. 84.

5 "Excogitaverat." Beckmann would seem to give this word the force only of "thought of," for he gives it as his opinion that attempts were made at Sidon to form glass mirrors, but that the experiments had not completely succeeded. "Had this invention formed an epoch in the art of making mirrors, Pliny, in another place (B. xxxiii. c. 45), where he describes the various improvements of it so fully, would not have omitted it: but of those experiments he makes no further mention." He also expresses an opinion that the Sidonian mirrors consisted of dark-coloured glass, resembling obsidian stone."—Hist. Inv. Vol. II. pp 69,70. Bohn's Edition.

6 Knowles says, in his Turkish History, p.1273, that in 1610, among other rare presents sent to the King of Spain from the Sophy of Persia, there were six drinking-glasses, made of malleable glass so exquisitely tempered that they could not be broken.

7 Dion Cassius and Suetonius tell a similar story; and, according to one account, Tiberius ordered the artist to be put to death.

8 This reading is doubtful. It would appear to mean "stone bandled." Another reading is "pterotos," "with winged handles."

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