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Glass has been around since 3500 BC, and since then, it has been one of the many everyday materials of choice. We pretty much see them everywhere nowadays--our windows, our windshields, our mirrors, our fancy wine bottles.

But now, it seems, glass is going to suffer some stiff competition from something that, until quite recently, exists only in science fiction: transparent aluminum.

But before finding out just how stiff the competition is going to be, let's look up the basic pros and cons of glass, in no particular order:

  • Glass lets light through, so that our houses don't look like caves on the inside.
  • Glass also focuses light, which makes for deadly heat-based weaponry.
  • Glass is transparent, so that we can see how we look.
  • Glass breaks easily, so unless you have a floor full of good, thick carpeting, you'd best find yourself another mirror.
  • Glass can't react well to pressure, which is why deep-sea submariners like Alvin have only very small windows.

So let us assume that in this alternate scenario, glass fell out of favor during the Industrial Revolution after an anonymous inventor accidentally discovered "transparent aluminum" (the name itself being a 20th-century last-minute addition). Would TA improve from the list above, or should we just stick with good ol' glass?

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    $\begingroup$ So is this transparent aluminum exactly the same as aluminum except that it lets light through? Do all other physical properties carry over? $\endgroup$ – Nex Terren Jul 10 '16 at 4:03
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    $\begingroup$ Focusing light not just allows heat-based weaponry, it more importantly allows photo and video cameras, telescopes and microscopes, and last not least glasses to correct your vision (although nowadays the latter is often plastics because it is lighter). $\endgroup$ – celtschk Jul 10 '16 at 7:16
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    $\begingroup$ I am a bit confused. Are you talking about metallic aluminium or of a compound like the answer so far addressed? $\endgroup$ – Johannes_B Jul 10 '16 at 11:11
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    $\begingroup$ "Glass is transparent, so that we can see how we look." Last I checked a mirrior was used to see what we look like because a mirror reflects light (the light that is reflected off ourself back to ourself), glass last i checked let light pass through it or am I missing something? $\endgroup$ – Mr.Burns Jul 12 '16 at 15:00
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Aluminium oxynitride aka ALON is the real world transparent aluminum. It's four times harder than glass, 80% transparent, and bulletproof up to and including a 50 caliber round. You can get it up to 18" x 35", a bit small for a window in a US house, but acceptable. Sounds great! Why are we still using glass?

It's expensive. How expensive? The manufacturer, Surmet, never gives a price. An article in Stars And Stripes from 2005 says:

Glass costs about \$3.25 per square inch, while ALON runs between \$10 and \$15 per square inch

The article goes on to elaborate why it wasn't being used in Humvees in 2005.

But in the long run, the new transparent armor could save money, La Monica said.

Because it is lighter than glass, it would put less wear and tear on Humvee engines and would save on gas, he said.

However, ALON has not been shown to be effective in large panels and is currently only suitable for small windows, a Defense Department spokesman wrote in an e-mail.

“ALON use in large windows will require significant investments in manufacturing technology and test and evaluation to demonstrate the required protection factors, especially against a multi-hit threat,” the spokesman wrote.

Countering the spokesman’s comments, La Monica’s supervisor at Air Force Research Laboratories wrote in an e-mail that “large size” is a relative term.

“ALON can be fabricated in 25-inch lengths, and it can be tiled to larger sizes,” wrote Ondercin. “In the opinion of this office [Air Force Research Laboratory Materials and Manufacturing Directorate at Wright-Patterson Air Force Base], the reason that ALON is not being used in Humvees is its cost. It can be fabricated in Humvee sizes, but it is costly compared to bullet-proof glass [layers].”

Ondercin wrote that Air Force Research Laboratories are trying to reduce ALON’s manufacturing costs to equal what it costs to put bulletproof glass on Humvees.

“This accounts for such items as wear and tear on vehicles due to the added weight and needed replacement due to permanent clouding of the glass in service due to sand abrasion from the use of the current glass product,” he wrote. “These issues would be greatly alleviated by the use of ALON, not to mention its greater ballistic protection.”

Why is it so expensive? It cannot contain any impurities, the crystalline structure must be perfect, and it must be polished for hours. If you're flying or driving in a combat zone this price might be worth it. But it's prohibitively expensive for your home or car.

Here's a great video about ALON.

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  • $\begingroup$ You say that it's expensive, which tells me that you didn't read the "glass falling out of favor during the Industrial Revolution", which was centuries ago. $\endgroup$ – JohnWDailey Jul 10 '16 at 13:24
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    $\begingroup$ @JohnWDailey I did read it, but you didn't say why it fell out of favor. Much of your scenario is left vague. You told us a lot about glass, but not about transparent aluminum. Others have asked for clarity and not gotten it. So I filled in those gaps with what I could find in reality. Fill in the blanks, please. Why did glass fall out of favor? How expensive is "transparent aluminum", in your universe, relative to glass? Does your "transparent aluminum" have the properties of glass, or of ALON, or something else? Don't answer here, please edit your question so everyone can see. $\endgroup$ – Schwern Jul 10 '16 at 18:20
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What you are talking about already exists: It's called Aluminium oxynitride. It's a ceramic made of aluminium, oxygen and nitrogen

However, glass is still widely used (And will remain so) because of how easy it is to produce it.

Glass is made of sand, which is extremely easy to obtain in large quantities. Aluminum, however? Much less easy to obtain in large quantities. Don't forget about the work it takes to to treat your aluminum and make it transparent, which drives the cost up.

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  • $\begingroup$ While you're right that AION hasn't replaced glass, in part, because it's expensive, it's not because Aluminum is scarce. Quite the opposite. Aluminum is the 3rd most abundant element in the Earth's crust. There's 80kg of aluminum in use for every human on the planet. It's so abundant we make about 300 billion soda cans a year out of it not to mention airplanes, cars, silverware, cookware, computer cases, bicycles, foil, light poles, heat sinks, pyrotechnics, coins, instruments... $\endgroup$ – Schwern Jul 10 '16 at 5:09
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    $\begingroup$ @Schwern I didn't say it was scarce, just harder than sand comparatively speaking. I did also mention the cost being higher. $\endgroup$ – Aify Jul 10 '16 at 5:51
  • $\begingroup$ You say that it's expensive, which tells me that you didn't read the "glass falling out of favor during the Industrial Revolution", which was centuries ago. $\endgroup$ – JohnWDailey Jul 10 '16 at 13:24
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    $\begingroup$ @JohnWDailey It's the process that's expensive. Even with our technology as it is RIGHT NOW, we haven't been able to reduce the cost. If your guy somehow managed to make it several hundred years ago, it probably would've cost him his entire neighborhood's net worth. Several hundred years later, the cost would drop to what it is right now - which is too high to even mention (As in you can't get a quote for it because it's too high). $\endgroup$ – Aify Jul 10 '16 at 17:35
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    $\begingroup$ @JohnWDailey "Materials that started out expensive are not so expensive in later years." That's not a universal truth. For example, copper is currently rather more expensive than it was in the past. Partly because we have to dig deeper for it, partly because we use so much of it (higher demand == higher price), and partly because of stricter controls on externalities like environmental controls and labor laws. We can't assume whatever your transparent aluminum is (you didn't say) just got cheaper over time. Time to fill in some blanks! $\endgroup$ – Schwern Jul 10 '16 at 18:26

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