How Much do You Know About Your Glass?

Glass today is pretty ubiquitous, to the extent that most of time we just look right though it without any thought. Yeah, that’s glass’s job, I get it, but it was a figure of speech. Anyway, there’s so much of it around us, and it facilitates so many things in our everyday lives, but how many of us have a clear idea of what it really is, how it’s made and where it came from?

So what is it, really? What’s in it? Typically, most basic glasses comprise various percentages of three crucial components: sand, potassium carbonate, and chalk or lime. What percentage those things come in really depends on what the glass is being used for, but, generally, it’s about 75% potassium carbonate, 24% sand, and 2% lime. Coincidentally, potassium carbonate is also used sometimes in soap, cocoa powder production, and as an ingredient in those delicious Chinese mooncakes with the fancy designs on them. Here’s the Wikipedia link, in case you need a rabbit to chase.

Most people would probably have guessed that, to actually make the glass, these three elements would be melted down into a molten-like form. And that’s exactly right. It can be heated any number of ways, so long as it reaches about 1000°-1600° Celsius. That’s hot. For those of you still clinging to standard measure like it really works (don’t worry, so am I), that’s upwards of 3000° Fahrenheit. Again, hot.

Once its molten, there are various ways to remove any impurities, including chemical additives and agitation. I’ll tell you, though, agitating a vat of viscous, sticky, 3000° incandescent sauce seems like a bogus plan to me.

With impurities gone, the burning goo can be drawn and rolled into giant sheets, for flat glass. Or, it can be pressed and blown, for hollow glass like light bulbs, fixtures, and fishbowls. Colored glass can be dies while in its molten stage, and it can also be printed or coated to achieve various colors. Mirrored glass is usually coated with a metallic, paint-like substance—mostly silver.

Considering the temperature at which this stuff is made, how long do you think it has to be cooled? Good question. It depends. The cooling time effects the final product’s brittleness and strength, but, generally, the slower the better. The strongest annealed glasses—those that aren’t subjected to further heat strengthening—can take up to several months before moving to other phases of production. I’m glad my pizza doesn’t take that long, because most of the time I barely have enough patience to wait for the cheese to cool. Man, I hate cheese blisters.

So how long has this whole process gone down? Well, a while. The approximate recipe we mentioned was probably drawn up by the Assyrians some time around 640 BCE, but we think glass has been produced as early as 8000 BCE, especially in Egypt, but maybe in Mesopotamia and Mycenae, China, and Northern Tyrol—a tiny little region of northern Italy and southern Austria.

Glass is obviously a lot different, and a lot more widespread today. But even as recently as the early Industrial Revolution glass was something of luxury. For example, you may have heard that in the late-17th century, the UK parliament imposed a window tax on its citizens across Scotland and England. Since glass was so expensive, having a lot of glazed windows was seen as an indication of prosperity, and thus the government felt added revenue could be extracted simply by adjusting taxes based on the number of windows a household enjoyed. The tax lasted until 1851—well into the Industrial Revolution—when it was repealed, as prosperity was no longer seen as a legitimate basis for increased taxation.

Now glass is everywhere. It’s easy and cheap to get, and we’re even coming up with new concoctions, like Gorilla Glass, by Corning, which uses alkali-aluminosilicate sheet glass stretched and flattened to be incredibly thin and almost unbreakable—almost. My old Galaxy 7, using the fourth generation of Gorilla Glass, didn’t quite make a shoulder-height tumble. Think we’ll have Gorilla Glass in our cars some day? Porsche does.

See you later.

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