Tile hardness; understanding the Mohs scale.
The Mohs scale of mineral hardness is a qualitative scale that characterizes the scratch resistance of various minerals through the ability of a harder material to scratch a softer material.
It was created in 1812 by the German geologist and mineralogist Friedrich Mohs.
A common requirement in our industry is to find out whether a tile is real porcelain or ceramic. You can use commercially available professional testing kits like the set depicted or do a Mohs test yourself using commonly available materials you can find around the house or office.
Hardness of some common items on the Mohs scale.
2,5-3 Gold or silver jewelry
3-3,5 Copper coin
5-6 B2b ceramic tile
5,5 Steel knife blade
6,5 Steel nail
7 B1a porcelain tile
7+ Hardened steel file
8,5 Masonry drill bit
9 Quartz crystal
How to test tile hardness in 5 steps.
1. Find a clean surface on the tile to be tested. This is the ‘unknown’.
2. Try to scratch this surface with the point of an object of known hardness, by pressing it firmly into and across your test specimen. For example, you could try to scratch the surface with the point on a crystal of quartz (hardness of 9), the tip of a steel file (hardness about 7), the point of a piece of glass (about 6), the edge of a copper coin (3), or a fingernail (2.5). If your ‘point’ is harder than the test specimen, you should feel it bite into the sample.
3. Blow or wipe off any dust. Examine the sample. Is there an etched line? Use your fingernail to feel for a scratch, since sometimes a soft material will leave a mark that looks like a scratch. If the sample is scratched, then it is softer than or equal in hardness to your test material. If the unknown was not scratched, it is harder than your tester.
4. Now repeat the test, using a sharp surface of the known material and a fresh surface of the unknown.
5. Most people don’t carry around examples of all ten levels of the Mohs hardness scale, but you probably have a couple of ‘points’ in your possession. If you can, test your specimen against other points to get a good idea of its hardness. For example, if you can’t scratch it with a copper coin, you know its hardness is between 3 and 6. If you scratch your specimen with a piece of glass, you know its hardness is equal to or less than 6 or 7.
Tiles are ‘vitrified’ i.e. ‘turned to glass’. Ceramic tile will be scratched by glass but not by a copper coin. Real porcelain can be scratched by quartz but not glass. You can buy quartz online, from new age shops, gemstone centers and some garden nurseries. A piece like the one depicted is perfect.
Below is a quick reference chart of the Mohs scale with common item equivalents.