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                                         Surface Treatments










               There are various kinds of surface treatments that are applied on either
               side of the spectacle lenses. In addition to anti-reflection coating which has
               already been discussed separately, many other types of surface treatments
               are done to enhance optical and / or physical properties of the lens. Optical
               properties can be enhanced by tinting, UV coating and mirror coating and
               the physical enhancements can be achieved by hard coating, hydrophobic
               coating, anti mist coating, anti fog coating and toughening.

               HARD COATING
               Resin lenses are basically from two families of plastics—thermosetting
               materials and thermoplastic materials. A thermosetting material is created
               in a mould by chemical reaction, the cross linking of molecules is very
               strong to form a rigid structure, and if they are subsequently heated will
               not soften. CR  and most other high index resin lenses used for spectacle
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                             Fig. 13.1: Different layers of coating on a lens
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