Watch glass

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Watch glasses have to be robust against scratching and rupture.

Scratch resistance is measured on the Mohs hardness scale in steps of 1-10. The following types of glass are used with watches:

  • Plexi / acrylic glass :
    (polymethyl methacrylate (PMMA)); 3-4 Mohs, little scratch resistance, but unbreakable. Scratches can be polished with special acrylic polishing paste. From this material extremely arched (domed) watch glasses can be produced.
  • Sapphire crystal:
    is an artificially produced crystal: 9 Mohs (close to diamond, extremely scratch resistant and break-resistant).