The instant the mass of soft metal was on the table a roller of cast-iron was passed very swiftly back and forth over it, spreading it to uniform thickness, and at the same time flattening it. "The thickness of the glass is gauged by the strips of iron on which the roller moves," explained Giusippe to Jean. "These can be adjusted to any thickness. Notice how rapidly the men have to work. The glass must be finished while it is hot, or there will be flaws in it. It is a rushing job, I can tell you." "But--but you don't call this stuff plate glass, do you?" inquired the girl in dismay. "It does not look like it--at least not like any I ever saw used as shop windows or for mirrors." "Oh, it is not done yet. But it is what we call rough plate. That's the kind that is used where light and not transparency is needed. You often see it in office doors or in skylights of buildings. To get the beautiful polished plate glass that you are talking about this rough plate must be polished over and over again. But before it can be polished it must first be annealed as rough plate. It goes into the annealing ovens right from this table and comes out all irregular--full of pits and imperfections. No matter how flat the casting table is, or how much care is taken, the surface of the glass after annealing is always bad. If it is to be made into polished plate it must be ground down first with sand and water; then ground smoother still with a coarse kind of emery stone and water; next ground again with water and powdered emery stone. After that comes the smoothing process done with a finer sort of emery and water. Last of all the sheet is bedded, as we call it, and each side is polished with rouge, or red oxide, between moving pads of felt." "Goodness!" ejaculated Jean. "Do you mean to say they have to go through all that with every sheet of plate glass?" "Every sheet of _polished_ plate," corrected Giusippe. "Rough plate does not need to be polished or ground down much. It is made merely for use and not for beauty. Sometimes to add strength, and help support the weight of large sheets, wire netting is embedded in them. Wired glass like this was the invention of an American named Schuman and it is used a great deal; the wire not only relieves the weight of the glass but serves the double purpose of holding the pieces should any break off and start to fall. Often, too, insurance companies specify that it shall be used as a matter of fire protection." "But I should think if plate glass--I mean polished plate," Jean hurriedly corrected her error, "has to be ground down so much there wouldn't be anything left of it. It must come out dreadfully thin."