In process of time, as human industry is ingenious in discovering, it was not content with the combination of nitre, but magnet-stone[2829] began to be added as well; from the impression that it attracts liquefied[2830] 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 Ophir[2831] 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 engraved[2832] like silver. Sidon was formerly famous for its glass-houses, for it was this place that first invented[2833] 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 flexible[2834] 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.[2835] This story, however, was, for a long time, more widely spread than well authenticated. 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,”[2836] the price of which was no less than six thousand sesterces!
CHAP. 67.—OBSIAN GLASS AND OBSIAN STONE.
Among the various kinds of glass, we may also reckon Obsian glass, a substance very similar to the stone[2837] which Obsius discovered in Æthiopia. This stone is of a very dark colour, and sometimes transparent; but it is dull to the sight, and reflects, when attached as a mirror to walls, the shadow of the object rather than the image. Many persons use it[2838] for jewellery, and I myself have seen solid statues[2839] in this material of the late Emperor Augustus, of very considerable thickness. That prince consecrated, in the Temple of Concord, as something marvellous, four figures of elephants made of Obsian stone. Tiberius Cæsar, too, restored to the people of Heliopolis, as an object of ceremonial worship, an image in this stone, which had been found among the property left by one of the præfects of Egypt. It was a figure of Menelaüs; a circumstance which goes far towards proving that the use of this material is of more ancient date than is generally supposed, confounded as it is at the present day with glass, by reason of its resemblance. Xenocrates says that Obsian stone is found in India also, and in Samnium in Italy; and that it is a natural product of Spain, upon the coasts which border on the Ocean.[2840]
There is an artificial Obsian stone, made of coloured glass for services for the table; and there is also a glass that is red all through, and opaque, known as “hæmatinum.”[2841] A dead white glass, too, is made, as also other kinds in imitation of murrhine[2842] colour, hyacinthine, sapphire, and every other tint: indeed, there is no material of a more pliable[2843] nature than this, or better suited for colouring. Still, however, the highest value is set upon glass that is entirely colourless and transparent, as nearly as possible resembling crystal, in fact. For drinking-vessels, glass has quite superseded the use of silver and gold; but it is unable to stand heat unless a cold liquid is poured in first. And yet, we find that globular glass vessels, filled with water, when brought in contact with the rays of the sun,[2844] become heated to such a degree as to cause articles of clothing to ignite. When broken, too, glass admits of being joined by the agency of heat; but it cannot be wholly fused without being pulverized into small fragments,[2845] as we see done in the process of making the small checquers, known as “abaculi,” for mosaic work; some of which are of variegated colours, and of different shapes. If glass is fused with sulphur, it will become as hard as stone.
CHAP. 68. (27.)—MARVELLOUS FACTS CONNECTED WITH FIRE.
Having now described all the creations of human ingenuity, reproductions, in fact, of Nature by the agency of art, it cannot but recur to us, with a feeling of admiration, that there is hardly any process which is not perfected through the intervention of fire. Submit to its action some sandy soil, and in one place it will yield glass, in another silver, in another minium, and in others, again, lead and its several varieties, pigments, and numerous medicaments. It is through the agency of fire that stones[2846] are melted into copper; by fire that iron is produced, and subdued to our purposes; by fire that gold is purified; by fire, too, that the stone is calcined, which is to hold together the walls of our houses.
Some materials, again, are all the better for being repeatedly submitted to the action of fire; and the same substance will yield one product at the first fusion, another at the second, and another at the third.[2847] Charcoal, when it has passed through fire and has been quenched, only begins to assume its active properties; and, when it might be supposed to have been reduced to annihilation, it is then that it has its greatest energies. An element this, of immense, of boundless[2848] power, and, as to which, it is a matter of doubt whether it does not create even more than it destroys!