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Part I: The Truth about Glass

Glass is one of the most useful materials we use today; it’s eco-friendly, endlessly recyclable and extremely durable. Glass has an interesting lifespan and is created by melting sand, soda ash, and lime and can be molded, pulled or pressed before it cools. While the world would be a completely different place without the existence of glass, many people don’t realize how much of an enigma the material truly is in the science world. Since glass is melted, manipulated and cooled, it begins as a solid, becomes a liquid, then cools and hardens. But does it ever really become a solid again? This question has stumped physicists and scholars for years.

One cause for confusion was an old Urban Legend stating that glass is a supercooled liquid that flows very slowly, with no crystalline structure. One reason this myth exists is because antique windowpanes, from churches and buildings, have said to be thicker on the bottom than on the top. The theory was that glass had to be a liquid, since the gravity over the years settled the glass, causing the bottoms to be thicker. The reality of the myth, however, is that there is no statistical evidence proving that these panes are truly thicker at the bottom. Furthermore, any explanation for the phenomenon would go back to the process of manufacturing the panes of glass; the Crown glass process. The Crown glass process essentially made it difficult to produce glass panes of the same thickness, which could explain some of the variations in thickness.

So how did this Urban Legend last for so many years, even making its way into textbooks and lectures? It’s possible that the myth originated from a book by a German physicist, Gustav Tamman, who was one of the first to study glass as a thermodynamic system. Tamman had labeled the material a “frozen supercooled liquid” and was possibly quoted by numerous scientists thereafter.

The behavior of melted glass as it solidifies is very different from crystallization, and until about 20 years ago, supercooling glass was the only process available. In physics, a solid is considered to be made up of crystalline, which left glass in a category of its own. This presented a sort of paradox to physicists, who weren’t sure whether glass would then be classified as a solid, liquid, plasma, or maybe even a fifth state of matter. Continue reading Part II:The Truth about Glass on our glass glass marker board blog, to find out more.

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