There are a variety of methods that can be used when it comes to the glass manufacturing process whether for industrial, scientific, or traditional purposes such as windows and drinking-glasses. The same three ingredients are used in most of these processes and these consist of sand, alkali-based sodium bicarbonate (or “soda ash”) and lime from limestone. The soda ash is used to lower the initial melting point, but it can make glass water soluble.
The addition of lime or aluminum oxide (has greater chemical stability) is a means to prevent the glass from becoming water soluble. Furnaces at temperatures around 2,500º Fahrenheit fuse these three ingredients together, and at this point other ingredients may be added to adjust brilliance and color. The glass is then cooled by several hundred degrees to allow it to be shaped whether by pressing, blowing, or drawing.
As it cools, the glass becomes easier to mold and shape. Throughout the molding and shaping process it is repeatedly reheated in order to add strength. This is referred to as annealing. Further tempering processes include reheating the glass and cooling it with sudden blasts of cold air. When it comes to shaping the glass, there are many methods. For sheet glass, float glass manufacture is the current production method used most often.
In this method, the molten glass is poured into tanks with melted tin on the surface. The glass floats on top of the tin and settles into smooth sheets. To maintain its colorless quality dolomite (at levels below 0.1%) is included in the process. The method used to make the glass for vacuum tubes, light bulbs and laboratory glassware consists of drawing molten streams of glass around a rotating metal cylinder as air is pumped in.
The processes and substances mentioned here are just a few of the many different methods and additives that are used in glass manufacturing to create the desired shape, hardness, and color of the glass all depending on its intended application.