What is Plate Glass?

I also use a type of glass called "Plate" glass. Plate glass is defined as "a type of glass which is cast in a solid plate, typically through a roller process. The resulting glass is extremely flat and free of distortions. This type of glass is often used to make windows, and it is also utilized in the manufacture of mirrors, tables, and other objects which require extremely flat glass. There are a variety of different weights of plate glass available, ranging from incredibly thick and highly durable plate glass to more delicate varieties." (source: wisegeek.com)

I usually distinguish standard home window glass from the thicker plate window glass that one would see used in commercial buildings. Plate glass can be seen in auto windows, tabletops, storefronts, showers, or as shelf glass. It is great to cast with since you have large pieces you can break and stack vertically in mold (slightly angled in towards the middle of the mold center) as opposed to the very small puzzle sized pieces of tempered glass.

Here is a video from YouTube showing how plate glass made.