What if you made a knife out of bulletproof glass? High hardness and toughness?

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St33L

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Dec 18, 2013
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As many of you know, some of the top bulletproof glass implements can impede small arms fire, as well as some explosives. Unlike typical glass, bulletproof glass "appears" to have both high hardness and toughness. So, what if we made a knife out of bulletproof glass?

Will it chip at the edges and thus not hold an edge well? Will it be comparable to, say, ceramic knives? Superior to ceramic knives?
 
Bullet proof has nothing to do with taking and ho!ding an edge. All it has to do with is stopping bullets.
 
There is no bullet proof glass. There is bullet resistant clear polycarbonate, but no bullet proof glass. Thank you.
 
AndreLinoge said:
There is no bullet proof glass. There is bullet resistant clear polycarbonate, but no bullet proof glass. Thank you.
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Yes, bullet resistant glass known (technically inaccurate) colloquially as "bulletproof". Thanks.

Danke42 said:
And you can hide it in water.
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+1

And in the air - whatever's on the receiving end literally won't "see" it coming lol...

And, you'd probably have to be aware of its presence when wielding so as not to cut yourself.
 
I worked with a fella who used to install tempered glass, and he told me a little-known fact.

Tempered glass is easy to break, if you hit it in the corner. I'm not sure why, but it's the reason why the emergency folks will rack a window in the corner to break it during vehicle extrication. One good tap, and it falls apart.

So your knife could not have any kind of point or angle on it.

Aren't there usually multiple layers also? Kind of a sandwich, held together by an optically perfect adhesive? That could make sharpening a challenge.

I like the idea, but if ultimate edge retention is your goal, the existing alumina-ceramic knives do an excellent job, without being so finicky about shock loading.
 
Neil Stephensen wrote Snow Crash, a novel where one of the chief antagonists used knapped plate glass knives and harpoons. It was a pretty cool concept plus the bad guy was an Aleut, which is my tribal affiliation--how could I not like it? Tempered glass reacts much differently to impact, in that it is designed to be frangible without tossing jagged shrapnel everywhere. When cars used regular glass, horrific lacerations were pretty much expected. In the 60s they experimented with a wafer of clear plastic sandwiched between two thin layers of class, which could result in actual decapitation in the event of forward ejection into the windshield; the plastic held all those nasty shards together as the victim was rammed onto them. Bulletproof glass is a thick polycarbonate polymer more akin to a plastic than silica-based compound, so it could be sharpened but it is doubtful that it would achieve the microns-thin edge of flaked obsidian. A knife made of either substance would be quite fragile compared to a metal knife of even iron or bronze.
 
I worked at a leading glass fabricator 10 years ago, i worked on the line that tempered and heat treated the glass, once we put a 6 ft my 12 ft piece of tempered glass on the ground and hit the corner, the whole thing shatters instantly into pieces about the size of a pinky nail. Guess who had to clean it, fun times. Ive also thrown some of the tempered test lites (what they call a piece of glass) into the metal trash bin right into the corner and it wouldn't break, tricky stuff. The bullet proof glass we made (not my department though) was a series of 5/8 inch tempered glass, vinyl laminate, and polycarbonate stuff. the key was layers, and the laminate, like in your windshield, we made those too. In the end each lite was about 2 inches thick or so, don't quote me on any of this because its been a long time and I only seen it when I was wondering around not doing my job.
 
Oh yeah, and if we didn't sand the edges of the glass round, it could spontaneously bust after the tempering process, so no edge with tempered, annealed glass would work a lot like obsidian though, its cut though my Kevlar suit from time to time.
 
Shorttime said:
I worked with a fella who used to install tempered glass, and he told me a little-known fact.

Tempered glass is easy to break, if you hit it in the corner. I'm not sure why, but it's the reason why the emergency folks will rack a window in the corner to break it during vehicle extrication. One good tap, and it falls apart.

So your knife could not have any kind of point or angle on it.

Aren't there usually multiple layers also? Kind of a sandwich, held together by an optically perfect adhesive? That could make sharpening a challenge.

I like the idea, but if ultimate edge retention is your goal, the existing alumina-ceramic knives do an excellent job, without being so finicky about shock loading.
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What we think of as "bulletproof glass" is really laminated glass, and very thick. It will stop certain bullets due to its mass and the layers of plastic hold the pieces together.

Tempered glass is made to break into little pieces and not do serious damage to people. It is heat treated to put the outside in compression and the inside in tension. This does make it more resistant to breaking under some conditions but once broken the internal tension makes it self destruct.
 
AndreLinoge said:
There is no bullet proof glass. There is bullet resistant clear polycarbonate, but no bullet proof glass. Thank you.
Click to expand...
Not an expert but isn't it multiple layers of poly AND glass? I would think the hardness of the glass plays a part. Much like trauma plates.
 
Straight polycarbonate has decent bullet resistance. Putting glass on the faces gives resistance both to scratches and to chemical attack. Washing windows entails both forms of potential damage.
 
BitingSarcasm said:
Neil Stephensen wrote Snow Crash, a novel where one of the chief antagonists used knapped plate glass knives and harpoons. It was a pretty cool concept plus the bad guy was an Aleut, which is my tribal affiliation--how could I not like it? Tempered glass reacts much differently to impact, in that it is designed to be frangible without tossing jagged shrapnel everywhere. When cars used regular glass, horrific lacerations were pretty much expected. In the 60s they experimented with a wafer of clear plastic sandwiched between two thin layers of class, which could result in actual decapitation in the event of forward ejection into the windshield; the plastic held all those nasty shards together as the victim was rammed onto them. Bulletproof glass is a thick polycarbonate polymer more akin to a plastic than silica-based compound, so it could be sharpened but it is doubtful that it would achieve the microns-thin edge of flaked obsidian. A knife made of either substance would be quite fragile compared to a metal knife of even iron or bronze.
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Didn't that guy ride around on a motorcycle with a nuke in the sidecar?? Man, I loved that book...must have read it over 20 years ago. Hiro Protagonist! hahaha. Thanks for the reminder...I might just read that one again!

fwiw, rumor has it they are working on a movie.
 
Ya, Raven from Snow Crash was his own sovereign nation thanks to his nuclear-armed sidecar. His tattoo of "poor impulse control" on his forehead is one I would like to slap on a few folks too, but I doubt we could get away with that. After Hiro's name, my second favorite thing was the uranium-powered minigun named Reason, because "everybody listens to reason." Loved the humor. Every 4 or 5 years they talk about making a movie and maybe one day it will happen, though I have no doubt that Raven would probably get changed into a blond Uzbekistani who kills with salad tongs instead of glass knives.
 
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