Crystal Manufacture

 By Bruce Shawkey

Found this interesting article in a 1960s issue of Europa Star magazine:

The very existence of the watch glass or "crystal" as it is sometimes called, gets to be forgotten by the wearer, and yet it has a vital function which is to protect the dial and hands and to prevent the penetration of any foreign matter Into the interior of the watch. The qualities that are expected from a watch glass are: clarity, resistance to shocks, impermeability. It must also be made of material that can be cut and turned accurately. For these reasons a brief glance at its manutaCture is interesting.

"Glass" is an incorrect term

One always speaks of the "glass" or "crystal' of a watch, but both these words are incorrect. Glass is no longer used or very rarely and has been replaced by newer products. Celluloid—cellulose nitrate hes also become obsolete; it is highly flammable. Its use presented serious drawbacks. For cheaper watches, a similar product Is now used called cellulose which although definitely combustible is much less dangerous. The material now currently used for watches is organic glass which combines most of the necessary qualities. As Its name indicates, it is a derivative of carbon, more exactly a synthetic thermoplastic resin of the methacrylic class. withstands changes of temperature, does rot under the effect of light, is not affected by alkaline solutions, diluted acids, benzine or similar products, largely eliminating cracking due to age or to the effects of tension engendered by fitting the glass into the bezel of the case. As it can easily be worked by means of a graving tool, grindstone, or file and polished, its shape can be modified under heat. Finally it is waterproof and often excellent resistance to shocks.