14. Whenever the glass has become too stiff, by cooling, for inflation, it is again softened by holding it in the blaze of the fuel, and the blowing is repeated, until the globe has been expanded to the requisite thinness. Another workman next receives it at the other end, upon an iron rod, called a _punt_, or _punting iron_, when the blowing iron is detached. It is now opened, and spread into a smooth sheet, by the centrifugal force acquired by the rapid whirl given to it, in the manner exhibited in the preceding cut. The sheet thus produced is of a uniform thickness, except at the centre, where the iron rod had been attached. 15. An inferior kind of window glass, the materials of which are sand, kelp, and soap-boilers' waste, is made by blowing the _metal_ into cones, about a foot in diameter at their base; and these, while hot, are touched on one side with a cold iron dipped in water. This produces a crack, which runs through the whole length of the cone. The glass then expands into a sheet somewhat resembling a fan. This is supposed to be the oldest method of manufacturing window or plate glass. 16. The window glass produced in the manner first described, is called _crown glass_; and the other, _broad glass_. But by neither of these methods can the largest panes be produced. The blowing for these differs from the methods just described, in that the material is blown into an irregular cylinder, open at its further end. When a sufficient number of these cylinders have accumulated, the end to which the blowing iron had been attached, is _capped off_ by drawing round it a circle of melted glass, and the cylinder is divided longitudinally by touching it through its whole length with a hot iron. The cylinders, in this state, are put into the annealing oven, where, by aid of a heat which raises the glass to redness, it is expanded into sheets. These sheets are then broken into panes of several sizes by the aid of a diamond and a straight edge, as in the case of glass blown by other methods. 17. _Casting._--Plate glass formed by the method last mentioned, is denominated _cylinder glass_; and it is used not only for windows, but also for mirrors not exceeding four feet in length. Plates of greater dimensions are produced by a process called _casting_. The casting is performed by pouring the material, in a high state of fusion, upon a table of polished copper of large size, and having a rim elevated above its general surface, as high as the proposed plate is to be thick. To spread the glass perfectly, and to render the two surfaces parallel, a heavy roller of polished copper, resting upon the rim at the edges, is passed over it.