What Goes into Glass?
The main ingredient in glass is sand (silica). An ancient Egyptian recipe to make glass mixed sand, limestone (calcium carbonate) and soda ash (sodium carbonate). This chemical mixture was heated to extremes until it became a liquid.
This process can still be used today, but there is no single chemical composition which characterizes all glass in our modern world. Thousands of different chemical compositions can be made into glass, and when other substances are added to the glassmaking formula, the final product is affected in various ways. Its color can be changed with metallic oxides: Adding iron will make create a strong green color, sulfur will provide a reddish hue; silver will give you a pale yellow tint. Other attributes can also be altered such as the glass' durability, thermal and reflective properties, and much more. Because of this, glass can be used in a variety of ways and for a variety of purposes.
But it's not just the ingredients that go into making glass that affect its properties. The way it is made also plays a role—how it is heated, cooled and shaped.
About Glassmaking and Glassblowing
Until about 50 B.C. glass objects could only be made slowly. One glass bottle could take several days to make by casting (used a mold), core forming, or cutting techniques. That situation quickly changed with the discovery of glassblowing. The Roman people discovered that an object could be formed by gathering molten glass on the end of a hollow blowing pipe and inflating it like a bubble.
This technique allows glass to be blown into hollow mold to be formed or freely shaped with simple tools on the end of the blow pipe. As long as the glass remains hot, it can be formed and molded into various shapes, but when hot glass cools, it slowly becomes stiffer and stiffer. Because of that, liquid glass is not like the other liquids; at room temperature, glass is so stiff, it is a very hard and brittle solid.
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