From the mind of Gabriel shear

Tuesday, December 10, 2013


broken glass

Disclaimer: Information presented here is for educational purposes only. The author and website are not liable for any damages caused by the misuse of this information .


Ninja Rocks

I learned about “Ninja Rocks” many years ago. I’ve always felt that it was a great idea. So I’m sharing it with you. Perhaps someday it might just help you out of a jam.

Just a little information first.

Breaking plate-glass, like the kind used in older windows, and in picture frames. Is a fairly easy thing to do. Other then the obvious risk of cutting yourself. You could punch through plate-glass with relative ease. Tempered Glass on the other hand is a different story, and you could easily break bones in your hand trying to break a tempered glass car window or sliding glass door.

Tempered glass is still just glass, but it’s received a treatment called “tempering”. Glass is tempered by cooling the outside of the glass quickly. While the inside is allowed to cool more slowly. This causes a compressive stress on the outside. While the inside is under tension. Which is why it seems to explode into tiny bits when it is broken. It is also why its called safety glass. This balance of compression and tension allows it to take shocks both physical and thermal far better the non-tempered glass.

Tempered glass can take quite a blow before breaking. Concentrated sharp impacts are the best way to break it and the harder the object the better. This is why emergency hammers for escaping a vehicle have a pointed metal end to break the glass.

A ninja rock can also break tempered glass, but with incredible ease.

“What are ninja rocks?” Your probably asking. Well, basically they’re just small pieces of the white insulator from spark plugs. (Simple huh.) You can break the insulator with a hammer or something similar. A piece of it the size of pea. Will shatter a car window into a thousand pieces. Simply by flicking it at the window.

How is this possible?

Well, let me tell you. The surface of the glass is hard, but the ceramic insulator is even harder! Made of sintered aluminum oxide. It is just under diamonds on the Mohs hardness scale. This is very hard stuff. Due to the internal stresses of tempered glass. A small scratch or cut to the outer shell of the glass. Can allow the high internal stresses to escape. Causing the glass to fracture rapidly. The ninja rock is a lot harder than glass and so will “scratch” the glass with ease.

You can easily carry a small ninja rock. In your wallet or purse, so that you will have the ability to quickly, and easily break tempered glass. If the situation  ever arises.


– Gabriel Shear



Leave a Reply