Watch and watch glass knowledge

- Apr 09, 2019-

Watch mirror is different from glasses and mobile phone screen, it is human wear on the wrist with the largest amount of physical activity, it is very easy to bump and rub with some hard objects in daily life, so it is also very easy to scratch. How to choose a kind of glass material which is wear-resistant and not easy to scratch? Today, most of Swiss high-end watchmaking brands will use sapphire crystal glass as the material of the mirror. Here we elaborate on some key points of knowledge about glass mirror, which may broaden your horizon.


1. What is watch crystal?


Watch crystal is a transparent covering used to protect the watch surface. It has been accidentally noted that the term "crystal" is also used to describe a very small part of a quartz table that is used on a swing. There is no connection between them. To avoid confusion, the latter is often referred to as "quartz crystal".


2. What is the watch crystal made of?


They can be made of any of the following three materials: 1. Plexiglass (a transparent and lightweight plastic); 2. Ordinary glass (used to make glass windows), usually called "mineral glass" in the watch industry; 3. Artificial sapphire (see question 4). Some crystals are made by combining minerals with sapphire glass. For example, some watches made by Seiko use crystals made from mineral glass covered with artificial sapphire. Seiko calls this synthetic material "Sapphlex".


3. What are the advantages and disadvantages of various materials?


As you think, plexiglass is the cheapest. It's also the hardest to break, but the easiest to scratch. Mineral glass, even though it undergoes a tempering process, is more fragile than plexiglass. However, it is more resistant to scratching than plexiglass. Artificial sapphire is the most expensive glass crystal material, but it is the most anti-scratch. Because it is too hard, it is more fragile than mineral glass or plexiglass.


4. What is artificial sapphire?


It is a very hard and transparent material, made of alumina crystallized at high temperature. Artificial sapphires are chemically similar to natural sapphires and can be used in jewelry, but do not contain colouring agents for gemstones. When it is heated, artificial crystals form spherical shapes, which are then sawn into sheets with a drilled saw. These discs are then polished and polished into watch crystals (one reason why sapphire crystals are relatively expensive is that the tools needed to make them are expensive). Sapphire, both natural and man-made, is one of the hardest materials on the planet, with a Mohr hardness of 9 (Mohr hardness is a system for evaluating the relative hardness of different materials, with diamonds having the highest Mohr hardness of 10). Surface crystals made of synthetic sapphires are usually marketed as "scratch resistant", which only means that they are difficult to scratch, but not impossible to scratch. Diamonds can scratch them, and those with Mohs hardness between 9 and 10, with silicon carbide added, are harder than sapphires, like diamonds, can also scratch them. Sometimes, these materials are used to make imitative gems on furniture or wall surfaces. Watch wearers should pay attention to the fact that if sapphire crystals are carelessly scraped onto the surface of such materials, they will cause scratches.


Unformed Sapphire Crystal Glass


5. Can you see with the naked eye that a crystal is made of sapphire?


No. Generally speaking, mineral crystals are like sapphires. One sure (though often impractical) way to distinguish them is scratch testing, says Johann Jorgo, New York technology director for Baume & Mercier watches. A stainless steel knife or wrench can scratch mineral glass crystals, but not sapphire crystals.


6. Is scratch resistant crystal new?


Not new. Artificial sapphire was invented in the 19th century and was used in watches in the 1960s. Not all high-end brands use sapphire crystals on their watches, at least some of them don't.


7. Are all scratch-resistant crystals made of synthetic sapphire?


No Some mineral glass crystals are also marketed as "scratch resistant". These crystals have hard coatings that help them reduce scratches.


8. These terms "lunette", "bombe", "cheve" and "boule" are sometimes used to describe watch crystals. What do they mean?


They are all French words related to crystal shape. "Lunette" is simply a circle, like a full moon (lune means "moon" in French). Bombe, cheve and Boule all indicate concave or dome-shaped. There are other terms used to describe the shape of a watch crystal. A "raised" crystal, with a flat top but raised upwards, is like a birthday cake. Shaped crystals are any non-circular crystal - rectangular, square and oval are the most common. The "Cocktail" shape is a more bizarre and extreme example of crystal shape. They include slender bread-shaped and octagonal crystals.


9. What is "anti-reflective" crystal?


One or both sides of the crystal are coated with a layer of material (as is the case with reflective lenses) to reduce the reflectivity and make the surface more readable. Antireflective crystals can be made from mineral crystals or synthetic sapphires. An interesting feature of these crystals is that they are almost invisible from the front because they do not reflect any light. In some cases, the coating gives the crystal a bluish tone.