When it comes to watch mirrors, in fact, everyone should know. It is a very important exterior part of a clock. Its function is to isolate water vapor and dust, in order to protect the hands, dials, and movement. But in the 16th century when the clock was invented, there was no watch mirror. Instead, it was covered with a cover, just like the old flip phone, or simply exposed. Later, watchmakers used transparent silicate glass as their watch mirrors. Of course, there were also natural crystals used to grind watch mirrors at that time. That was a relatively tyrant's behavior.

Glass is the longest used surface mirror material. It has been used for hundreds of years. However, as we all know, silicate glass is not only fragile, but also prone to scratches. In the first half of the twentieth century, the original silicate glass was upgraded to quartz glass, which improved the scratch resistance and abrasion resistance. In the 1940s, a revolutionary surface mirror material "acrylic" appeared on the stage. Acrylic, also known as PMMA or plexiglass, is derived from English acrylic (acrylic plastic), and its chemical name is polymethyl methacrylate. Although this material is still prone to scratches, it is not easy to break compared to quartz glass and silicate glass. Because of this advantage, acrylic crystals quickly replaced glass crystals.

The mirrors of antique watches are mostly arched. Because the acrylic mirrors are pressed by the pressing process, they can be stamped arbitrarily after heating the raw materials, and it is easy to create a curvature, which is later called "bubble mirrors" by watch friends. And another advantage of the acrylic table mirror is that it can be easily processed later, and can be modified with sandpaper or a file.

Later, with the development of the glass industry, a mineral glass appeared. The difference in mineral glass was that alumina was added during smelting, and chemical and heat treatment were also carried out in the later period. These processing methods reduce fragility.

After the 1970s, sapphire crystals began to be used. sapphire watch glass，In modern times, except for a few retro watches that use plastic acrylic crystals, most high-end watches are sapphire crystals. Although sapphire is an artificial gemstone, it has a Mohs hardness of 9, second only to diamond, and is mainly scratch-resistant.

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