You can see through it, drink from it, make boats from it or play marbles with it. Glass is one of the most common man-made materials and has been in use for over 5,000 years. According to a Roman story, Phoenician sailors camped one night on a beach, lit a fire and set their cooking pots on blocks of natron (soda), which was the cargo they were carrying. When they woke the next morning they found that the heat of the fire had fused the sand and soda into glass. The story may be false, but the formula is correct. Sand or silica is the main ingredient of glass; soda is added to bring down the melting point and a third ingredient, lime, is used to make the product hard and durable.

Glass is an amorphous substance made primarily of silica fused at high temperatures with borates or phosphates. Glass is also found in nature, formed when hot lava quickly cools after oozing to the earth’s surface (obsidian), or by lightning striking a beach or desert (fulgurite). There are also tektites, which are small, rounded bodies of glass formed as a result of meteorites crashing to earth. Primitive man used obsidian and fulgurite to make knives and arrowheads.

Glass is called amorphous because it is a non-crystalline substance (it is neither a solid nor a liquid but exists in a vitreous, or glassy, state). When it cools its atoms remain in the same random arrangement as in the liquid but with sufficient cohesion to produce rigidity. This is the reason for its transparency. It is sometimes referred to as a super-cooled liquid. Molten glass can be shaped by means of several techniques. When cold, it can be carved but at low temperatures it is very brittle.