Much care is necessary in handling these large plates, and every attention is necessary and devoted to get the largest pieces of plate without defects. All portions showing defects have to be cut away, and, consequently, reduce the size of the plate when finished. In another method of making plate glass the molten metal is fed between two or more parallel rollers, which are spaced apart to the thickness of the glass required (about 1/4 in.). These rollers squeeze the glass out to a uniform thickness. A roughly decorated surface is sometimes given to this glass intentionally, by the metal rollers being indented with some form of set star pattern. This glass is not ground or polished, and is sold under the name of muffled or cathedral glass. It is mostly used for roof lighting, where the transparency may be somewhat obscured. Wired glass, or strengthened plate, is formed by embedding in the soft glass, whilst being rolled, a network of metallic wire of special composition to suit the temper of the glass. This wire is fed from a separate roller into the space between the parallel rolls as the hot metal is fed in from either side. It is necessary that the wire should be made from a metallic alloy which is not easily oxidised. Another method of strengthening plate glass consists in sealing together two plates with an intersecting film of celluloid. A decorated coloured rolled plate is made for use in leaded lights by mixing portions of several differently coloured glasses together in a small pot and slightly agitating the contents so as to intermix the respective colours. When the glass is rolled out, a pretty agate or marbled effect is obtained, due to the distributed coloured glasses becoming intermixed. As a rule, these glasses are more or less opalescent, and are only used for decorative purposes, church lights, etc. ------------------------------------------------------------------------ CHAPTER XIII TUBE, CANE, AND CHEMICAL GLASSWARE Laboratory and chemical glassware consists of thin blown ware in the form of flasks, beakers, test tubes, etc., used in chemical operations. Most of these goods are blown in hinged moulds mechanically or automatically operated by the worker. The lips and flanges of the necks are neatly formed afterwards by re-heating and working the edge to a form allowing them to pour cleanly, and prevent any fluid contained therein from running down the sides of the flask or beaker whilst in use. The heavier glassware, in the form of desiccators, measuring cylinders, specimen jars, and three-necked bottles, are made by handwork. Chemical apparatus has necessarily to be made from a permanent stable highly refractory glass, so as to resist the solvent actions of mineral acids, alkaline solutions, and boiling water, as well as sudden changes in temperature.