Even though diamond-coated cutting tools are used to cut or score glass, diamond isn't the only material able to cut and scratch glass. Anything harder than glass can scratch it -- sometimes even everyday outdoor dust.
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Minerals, rocks and metals are compared to one another with the Mohs Scale of Hardness, developed by mineralogist Frederich Mohs in the early 1800s. At its simplest, the scale ranks 10 readily available minerals from softest to hardest. Talc, the softest mineral, ranks a 1 on this scale, with diamond ranking at 10. Quartz, a 7, is a mineral comparable to glass in terms of hardness, while it is also the most abundant mineral on earth. Glass ranges from 6 to 7 on the Mohs scale, depending upon how it's made. Every item ranked on the Mohs scale can be scratched by an item higher up on the scale; for example, copper -- a 3 on the scale -- scratches talc easily, while glass scratches copper.
Things That Scratch Glass
Anything harder than glass can scratch it. Because quartz is so abundant on this planet, it's also in dust outdoors at times. This is why wiping off eyeglasses made of glass on a windy, dusty day may scratch them, although it may take some time to notice the tiny nicks. Hardened steel, such as a file, can scratch glass. Titanium, chromium and even sapphires or rubies can scratch glass, while aluminum or a butter knife blade may not.
While some old commercials showed a diamond edge cutting a round hole in glass, diamond isn't the only material used to cut glass in practical applications. Glass-cutting tools usually have carbide wheels, which are as hard or harder than diamonds. Drilling through glass -- essentially "cutting" a hole through it -- also requires a special glass-cutting bit, usually coated with diamonds, as the glass is harder than a basic steel drill bit. Because glass is also brittle, cutting thin pieces of glass -- even bottles -- typically involves scoring it first with a glass cutter, and then snapping the glass along the scored line.
Always wear safety glasses and take the proper precautions when working with glass.