The glasses for watches can be in 3 groups. Plastic lenses, mineral glass and sapphire glass. Each of these types has different characteristics, different application areas and also various fashionable aspects. There is also within these groups different quality standards in the following should be clarified.
also Hesalithglas, acrylic or Plexiglas called – consists of the plastic polymethylmethacrylate (PMMA). They are relatively lightweight and impact resistant. Disadvantage of plastic glasses is their low hardness, so they are easily scratched.
The chemical name for mineral glass is silica SiO2. Good Mineralgäser are not simple window glass. The surface is good mineral glass in the manufacture in a complex procedure chemically hardened. Mineral glasses are much harder than plastic glasses, they are not osmotically and not yellow. But there is also mineral glass damage. Is particularly detrimental when a fraction small glass splinters in the movement reach and cause damage there.
The hardest among Uhrgläsern is undoubtedly the Saphirglas. Sapphire crystals are synthetically by the Verneuil process produced. A small drawback of the sapphire crystal is to increase light refraction of this mineral. It may be more disturbing reflections on the watch shows. Therefore, high-quality sapphire crystals in watches also reflective.