38

PROCESS OF CASTING.

the same thickness as the plate of glass is intended to be: the ledges are to confine the fluid glass to the size proposed. A heavy copper roller then passing over it, pushes the soft glass before it, and presses it into a smooth, level surface. The newly formed plate, when sufficiently hardened by cooling, is slid into a furnace, or kind of oven, where it remains for a fortnight; care being taken that it should cool very gradually.* The plates thus formed are afterwards ground to a more exact level with sand; and then polished with emery, tripoli, and putty, till they acquire that beautiful surface we are accustomed to see. †

I have said, that we are indebted to the ingenuity of the French for the art of casting plates of glass. At Ravenhead, in Lancashire, they are now cast in such perfection as to equal, in every respect, those that are made in France. A number of persons have formed themselves into a company, to defray the great expense and share the profits of the undertaking. They

* Lardner, ib. 203. + Grey s Op. Chem. 561.

Ency. Brit.

GLASS-WORKS AT RAVENHEAD.

39

have an iron casting-table fifteen feet long, nine feet wide, and six inches thick. This enormous table is so heavy that it is supported on castors, for the convenience of moving it close to the mouth of the ovens, in which the plates of glass are to be gradually cooled.

The room in which this great table stands, is said to be the largest under one roof that has ever been built in England. It is even larger than Westminster Hall, being three hundred and thirty-nine feet long, one hundred and fifty-five feet wide, and proportionably lofty. The melting furnaces are ranged down the middle, and occupy about one-third of the apartment, The ovens, in which the glass plates are gradually cooled, are placed in two rows, along the side-walls of the room. Each of them is sixteen feet wide and forty feet deep. Their floors are just level with the top of the great casting-table; so that when all is ready, the table may be rolled up to the mouth of the oven, and the plate slipped in without delay.

It is a great favour to obtain admission to a

40

PARKES'S DESCRIPTION.

plate-glass manufactory. Mr. Parkes, who was permitted to witness the casting of a large plate, describes it as a grand and interesting sight. A vast body of melted glass, of the finest and purest materials, is poured at once from an immense crucible; when the large copper roller has passed over it, the glass is spread out into a sheet of uniform breadth and thickness, and its surface exhibits a variety of colours. At least twenty workmen are employed in the operation. All are busy; but there must be no bustle-no disturbance of any kind: even the opening or shutting of a door must be avoided, till the glass is tolerably hardened, lest the motion of the air should cause a wave or wrinkle on the surface, and thus lessen the value of the plate.*

We will, if you please, leave our plate to cool in the oven, as it is quite time that I should relieve your attention. It would be a pity, in seeking to amuse you, to make you feel like the Esquimaux who were taken to see London. When they returned home, they sat down with

* Lardner, 196, 203.

their elbows on their knees, and hid their faces between their hands: they seemed quite melancholy and stupified. They would answer no questions: they would say nothing but, "Too

If you wish to hear any more respecting glass, I shall be happy to see you another evening. We will now take warning by the Esquimaux, and leave off before you have had "too much."

* Edgeworth's Practical Education, Vol. I. p. 118.