MOHS SCALE

The Mohs scale is an empirical classification of mineral hardness, established in 1812 by the Austrian mineralogist Friedrich Mohs. It is based on ten reference minerals, from talc (1) to Diamond (10), each capable of scratching all those preceding it. In watchmaking, this scale is fundamental for evaluating and selecting Materials. Sapphire and Ruby / Jewel synthetics (corundum, hardness 9) are used for watch crystals and jewel bearings precisely because they resist most common abrasives. Diamond (10) is used in machining tools and the finest Polishing tools. Steel components ranges between 5 and 6, gold between 2.5 and 3 — which explains its sensitivity to scratches. Knowledge of this hierarchy also guides the choice of polishing pastes: thus, a corundum powder should never be used on a Glass (crystal) sapphire, at the risk of permanently damaging it.