Sheet Glass is made by drawing the glass vertically out of the liquid mass, with the sheet so formed being fire polished and annealed. The drawing process produces waves and surface distortions that vary throughout the draw. Selection of cut sheets is made and classified AA, A, B, or Greenhouse solely on the optical qualities of the sheet. Polished Plate Glass is produced by rolling a continuous sheet or by casting and rolling large sheets separately. After annealing and cooling, the surfaces are made flat, parallel and bright by mechanical grinding and polishing.
Plate glass is available in three grades, also based on optical properties.
In the Float Glass process the molten glass floats on the dead flat surface of molten metal where it flows to a uniform thickness. When the sheet is drawn off, both surfaces are flat, parallel, fire polished and sufficiently cooled to remain undamaged by the rollers used to transport it through subsequent operations. This glass combines the optical quality of polished plate glass with the surface advantages of sheet glass. Rolled Glass includes patterned, corrugated plate glass blanks and wired glass. As the glass is drawn horizontally from the tank, figured, textured or plain rolls impress the desired pattern on one or both surfaces, regulating at the same time the thickness of the sheet.