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Shattering Glass Myths, Part 1 of 3

Updated: Jan 31, 2021

Think you know enough about glass? Well, read on. In my first of three blog installments, I'll explore some common misconceptions about glass. There's always more to learn.

Myth #1: Glass is a solid

I know it feels like a solid, especially if you bang your head against it. But actually, among glass artists and those who formulate it, glass is known as a super-cooled liquid--even when it feels solid. According to art-glass manufacturer Bullseye, its molecular structure, which is random, is one of the main reasons glass is considered a liquid. Bullseye's "Tech Notes 4" points out that below 1,000 degrees F, glass "behaves like a solid." Did you get that? Behaves. Still think I'm pulling your leg? Next time you're out and about, go find some old windows still framed to look at. You'll see, if you look closely, that the glass at the top of the pane will be thinner than glass at the bottom of the pane. If the window is, say, 100 years old or more, the glass has actually run toward the bottom of the frame, but very slowly. Solids do not behave this way.

Myth #2: Glass is glass--it's all the same

Window and mirror glass, bottle glass, Pyrex, art and stained glass--these are all very different kinds of glass. In fact, there are many more types than I'll mention here now, so I will expand on this idea in a later blog post. But for now, here are two possible ways to distinguish one type of glass from another: 1. COE (Coefficient of Expansion), and 2. The formula and purpose of the glass. COE, in over-simplified terms, is the rate at which a given glass will expand through its heating cycle, and in the glass world, the general idea (though it is over-emphasized and misused, according to Bullseye), is that artists should use glass of the same COE number in their art pieces. Mixing COE numbers causes breakage. Sounds simple enough, right? It isn't. Even glasses with the same COE number but made by different manufacturers have been known to fail when combined. Add to that the fact that not all glasses have the same viscosity (resistance to flow); a black solid color will heat faster and move more than a white or vanilla opaline. The second way glasses can be categorized is by their use, which changes the formulas or how they are assembled. Pyrex is harder glass than mirror or "float" glass, and tempered glass has stress built in deliberately, and that very stress is what makes it strong. And like the wines in them, bottle glass is notoriously unpredictable. So all glass is not the same--far from it!

In Part 2, we'll look at two more myths about glass's raw materials and a movie's misconception.

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