Many companies are now shouting about their hardness. They claim 7H or 9H or diamond hardness. What is the hardness fuss about? Let’s review.
Hardness is actually quite difficult and complex to measure, and there are many ways to investigate hardness. Actually to measure hardness, according to Wikipedia and my physic teacher:
That just means to measure hardness many aspects must be look into. For example the force or weight of one object striking or scratching another. And to make it all the more complicated, there are different industrial and scientific ways to measure each one of these elements. Also, because different industry seek a particular set of answers to their particular and important questions. Like, if i drop it, will it crack?
A typical hardness test won’t work as the hardness must include the elastic stiffness element. To satisfy all the needs from science and industry, various tests have been designed.
Here is a short list of some main tests:
- Vickers hardness test
- Brinell hardness test
- Hardness of ceramics
- Schmidt hammer
- Roll hardness tester
- Tablet hardness testing
- Persoz pendulum
Now, back to the hardness tests used more and more by car coating companies. (this was started by paint and the furniture business almost a 100 years ago) is the pencil hardness test. (I have written about this here.)
The simple problem is that the scratch test makes little or no sense. In the test, a pencil is put into a small “tester” on wheels. It rolls against the surface and the force of the pressure is set at 750 grams. That’s all. So, it only measure the scratch resistance from a very light object. Actually, almost no force is applied; hence, no knowledge of real life situation (like a stone flying into your paint) is gained.
This is not to say that it is bogus, as it does tell you that the car coating is 6H or something, but this information doesn’t mean that water marks, bird poo, stone chips, keys or even fingernails (opening the door) will not harm you car…as they will if you are not careful.
Some claim incorrectly that 7H is harder than steel. Remember graphite is 1H, and graphite is 70% of a pencil while the other 30% is made up of clay (and clay isn’t even on the Mohs Scale of hardness.
So, it is only with so me convoluted logic that pencils are harder than steel. Give me a crowbar and watch that pencil smash. Steel is harder than pencil with my new smash test.