# Glass Vs. Transparent Aluminum

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?

• So is this transparent aluminum exactly the same as aluminum except that it lets light through? Do all other physical properties carry over? – Nex Terren Jul 10 '16 at 4:03
• 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). – celtschk Jul 10 '16 at 7:16
• I am a bit confused. Are you talking about metallic aluminium or of a compound like the answer so far addressed? – Johannes_B Jul 10 '16 at 11:11
• "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? – Mr.Burns Jul 12 '16 at 15:00

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.

• 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. – JohnWDailey Jul 10 '16 at 13:24