Sea-wrack, or Sea-ware, a marine plant growing on the sea-coasts.—The sand used in the manufacture of glass is found at Lynn, in Norfolk, and Maidstone, in Kent.
These various articles are first carefully washed, and, after extracting all the impurities, they are conveyed to the furnace in pots made of tobacco-pipe clay, for the purpose of resisting the fire. Here the mixture is fused, and disposed of according to the different kinds of glass intended to be manufactured.
Round glass, such as phials, drinking-glasses, &c. are blown. When the different materials are sufficiently liquefied, the workmen dip long iron pipes into it, and blow the metal till it lengthens like a bladder. It is then rolled on a marble slab to polish it, when it is blown a second time, in order to form it into the shape of a globe. Next, it is cut off at the collet, or neck, adhering to the pipe: for this purpose, the latter is rested on an iron bar close to the neck, and a drop of water poured on it, by which means, it is cracked about a quarter of an inch, when it is slightly struck, or cut by a pair of shears, and immediately separated.—Now the workman dips the rod or pipe into the melting metal, whence he draws out as much as will connect the glass already made, to which he fixes the rod, opposite the opening caused by the breaking or cutting of the neck. In this position, the glass is carried to the mouth of the furnace, in order to be heated, or scalded: thus it becomes so soft, that it may be pierced, opened, and moulded at pleasure, without any apprehension of its breaking. The vessel, however, is not finished till it has again been returned to the mouth of the furnace, where, after being thoroughly heated, and turned quickly round, it will open to any size, by means of heat and circular motion. Should any impurities remain, they are cut off with the shears, as the glass continues flexible till it becomes cool. And, if the vessel thus made require a foot or handle, or any other ornament, the operator forms them separately, and unites them by the help of hot metal, drawn from the pots with the iron-rod:—the last operation for completing the glass, is that of Annealing.—See vol. i. p. 65.
Window or Table-glass, is worked nearly in the manner above described: the workman blows and manages the metal, so that it extends two or three feet in a cylindrical form. It is then carried to the fire, and the operation of blowing repeated till the metal is stretched to the dimensions required, the side to which the pipe is fixed diminishing gradually till it ends in a pyramidal form; but, in order to bring both ends nearly to the same diameter, while the glass continues flexible, a small portion of hot metal is added to the pipe; the whole is drawn out with a pair of iron pincers, and the same end is cut off with a little cold water as before.
The cylinder thus open at one end, is returned to the mouth of the furnace, where it is cut by the aid of cold water, after which it is gradually heated on an earthen table, in order to unfold its length, while the workman with an iron tool alternately raises and depresses the two halves of the cylinder: by this process, the latter accommodates itself to the same flat form in
