What does 9H mean?
9H refers to the hardest rating on the Wolff-Wilborn pencil hardness scale.
"A pencil is held at an angle of 45º and pressed hard into the surface until the end of the pencil breaks off. The coating is rated for the hardest pencil you can use without the surface marking."
This may sound a little odd, but it is a genuine scientific measurement. Of course, you can't use just any old pencil, you have to use very expensive scientifically calibrated pencils which comply with DIN ISO 15184. The pencils themselves are calibrated using the Mohs scale, which its self may use an "H" suffix as 1H to 10H, to determine hardness. However, it is important not to confuse the two, 9H on the Mohs scale is far harder than 9H on the Wolff-Wilborn scale. A calibrated 9H pencil seems to be somewhere around 2.5 on Mohs scale, which is about as hard as your fingernails.
Different industries appear to use this test in different ways, some have a mouse which holds the pencil at 45º which is then dragged across the surface of the coating, others hold the pencil and press down, which may be more suitable for field testing on upright surfaces.
When ceramic coatings first took the world by storm, the marketeers used the fact that their product was rated 9H as a selling point. However, as all the ceramic coatings are rated 9H, this does little to help one brand differentiate it from the others, and so it is something that is bragged about a little less now.
Written by Danny Argent. Last updated 19/01/2023 16:50