Glass Coating on Watches

2019-10-11

Any glass produces reflections, including flat and radian glass. Therefore, in order to reduce reflections and increase transmittance, many watches need to be coated on the glass.


The surface of the coated glass will show a light blue-purple color. Generally, MgF2 is used for coating treatment. The refractive index of MgF2 is 1.38, which is far lower than that of ordinary glass and lower than that of sapphire glass. The higher the refractive index, the stronger the reflection. Therefore, the effect of sapphire watch glass coating will be better. Among the available optical thin film materials, the refractive index of MgF2 is the smallest. The reflectivity of light can be reduced from 4% to 1.8% by coating with MgF2, which increases the transmittance at the same time. Of course, in order to improve the transmittance, multilayer coating can also be used to enhance the transmittance, that is, both sides of the glass are coated. Especially for watches with large glass diameter and radian, it is more necessary to increase the coating treatment. The coating can not completely eliminate the reflection, but can only reduce.


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The Mohr hardness of MgF2 crystal is grade 6, which is general hardness, but because of the thin film thickness, it is easy to wear out. The coating on the common glasses is very easy to be worn off, which also depends on the specific use. For example, when the glasses are washed only with detergent and water at ordinary times, the retention time is much longer than that wiped directly with cloth, and so is the watch glass.


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Watch glass inner coating will not be worn, when the glass coating damage, careful look will have a pattern of mottling, but also need to pay attention to watch in long-term storage, we must pay attention to moisture-proof, long-term wet environment, glass surface will be mildewed, but also destroy the coating. Therefore, it is important to keep desiccants and to avoid dampness in the case.