The pot is then removed from the furnace, and carried on a truck to an iron table or bench, having a flat surface about 18 feet long and 10 feet wide, two bars of iron of equal thickness to the desired plate are laid upon the face of the table near the edges. The fluid glass is poured on the table and spread with iron or copper tools; an iron roller about 15 inches diameter, equal in length to the width of the table, and weighing about 30 cwt. is rested upon the two iron bars and traversed over the face of the glass, to roll it out like dough to a uniform thickness. To insure the rotation of the roller in a straight line along the plate, it is provided at each end with toothed wheels that work in corresponding racks fixed on the sides of the iron table, and the roller is drawn along the table by means of two chains, coiled around the ends of the cylinder and worked by a windlass.

When the glass has been rolled flat, the cylinder is received at the end of the table upon two arms counterpoised by means of levers placed beneath, so as to allow of the heavy roller being raised or lowered by two or three men. The plate still red hot and yielding, is slid from the table upon the flat surface of a carriage which is wheeled to the annealing oven, upon the bed of which the plate is pushed and allowed to remain for several hours to cool gradually.

The plates when cold are examined as to their condition, and such plates as present defects in the glass, or irregularities in the surface that it would be tedious to grind out, are cut with the diamond into smaller pieces, but the nearly perfect plates are kept as near their full size as possible, and merely squared on the edges.

The plates of glass now measure about half-an-inch thick, and the surface is full of small irregularities, presenting a mottled appearance, the roughest side being generally that which was placed downwards upon the bed of the annealing oven, and copied all the irregularities of the bricks of which the bed of the oven is formed. The side of the glass that was uppermost in the oven, is comparatively smooth and bright from the action of the fire, although in many cases this surface is not so nearly flat as the lower. The plates have therefore to be ground flat and polished on both sides, formerly this was effected entirely by hand, but of late years the rough grinding with coarse sand, and the polishing with crocus, are almost always done by machinery, and hand labour is only resorted to for the intermediate process of smoothing with fine emery.

The grinding and polishing machines employed for plate glass differ somewhat in construction in various manufactories, but a single example of each will sufficiently explain the general method.

The grinding machines employed for the largest plate glass are arranged in pairs along the grinding room; every pair of machines is driven by one central beam, and consists of two benches of stone 15 feet long, 8 feet wide, and 18 inches high, placed about 10 feet asunder; upon each of these benches one or more plates of glass are embedded in plaster of Paris, close together, and quite level. Other plates of glass are cemented upon the lower faces of two swing tables or runners, which are traversed over the fixed beds, by a horizontal frame or beam about SO feet long; the machinery for driving the beam is fixed in a frame about 6 feet square and 18 inches high, placed between the two grinding benches. A horizontal shaft fixed underground, extends throughout the length of the grinding room between the lines of benches, and the motion from the shaft is communicated to every pair of machines, by a pair of bevil wheels leading to a central crank that revolves horizontally, and has a radius of about 2 feet; the arm of the crank is attached by a pivot to the center of the horizontal beam. Four other cranks of the same radius are placed parallel to the central driving crank, one at each corner of the square frame, and serve to guide the traverse of the horizontal beam, which is thus swung in a circle of four feet diameter in a manner somewhat similar to the grinding bed for marble, fig. 1099. The beam is supported at various parts of its length by chains suspended from the roof of the building, which allow of the traverse of the beam, and serve for raising it by means of levers for the removal of the work.

Near each end of the beam is attached, with the power of adjustment for position, a small sliding frame carrying bearings for the reception of the central pivot of the swing table or runner, which consists of a strong frame of wood covered with boards, and measuring 8 feet long and 6 feet wide, placed face downwards upon the bench; a central pivot stands up from the back of the runner, and enters the bearing fixed on the horizontal beam, which thus communicates a circular swinging motion to the center of the runner, exactly the same as that of the driving crank; and the runner being free to revolve upon its pivot, acquires a continual rotation around its own axis. By the combination of the two movements the relative position of the fixed bench and runner are continually changing; this tends to the mutual correction of the two surfaces of the glass, and greatly assists the equal distribution of the sand and water used in grinding. The horizontal beam makes about fifty circulating strokes in a minute, and the runners revolve upon their own axes about once to every five or six strokes. The position of the runners upon the driving beam is shifted once or twice during the grinding, to distribute the action as uniformly as possible over the entire surfaces of the glass plates.

The largest plates of glass are nearly equal in size to the fixed bench, and these are imbedded singly upon the bench with the most irregular side upwards; but more generally plates of medium and small size are ground together; they are selected of uniform thickness, and arranged close together upon the bench, with the largest plates in the middle and the smallest at the ends. The runner is covered by one or two plates at most, as small pieces would be liable to be thrown off by the centrifugal force.