There are four main raw materials used to make glass: silica sand, soda ash, dolomite and limestone. In many cases, broken pieces of glass called cullet are also added to these raw materials to help them properly melt when heated.
There are a number of different ways to make glass, depending on the desired finished product. No matter what type of glass is being made, the process begins with slowly heating all of the raw materials in a furnace to approximately 2,550 degrees Fahrenheit until they melt. The melted materials are then rapidly heated to a temperature of 2,800 degrees to allow the raw materials to fully mix together.
At that point, sheet or plate glass is made by allowing the melted raw materials to flow out of the furnace and onto a bed of molten tin. From there, the melted glass is left to slowly cool on the molten tin, which changes the structure of the glass to make it much stronger and to enable it to be cut.
The molten glass can also be formed in other ways, such as by blowing air into the glass, which is often used to make cups, beads and other types of glass ware.