Watch glass - About the watch

Glass

Face shield glass and its protector are against water, dust, etc. There are three main types of glass that are widely used today, including:

- Acrylic

Acrylic, a plastic-like material, is the cheapest type of glass while still being transparent. However, it has a high likelihood of getting scratched and being susceptible to damage. This material is more flexible compared to other crystals such as blue sapphire. Subcategories within this category include:

Compressed PVC (Polyvinyl Chloride):
This compressed material is not resistant to scratches and heat, easily getting scratched when it comes into contact with sharp objects. However, it has high resistance to pressure and only breaks under severe impact. Heat also causes a change in color for this type of glass, which can also change over time.

Application: This type of glass (acrylic) is mostly used in children's watches, and its high-quality version is used in sports watches, both made entirely of plastic. Nowadays, it is also used in fashion watches made entirely of plastic.

- Mineral

Mineral crystals are a simple structure of glass and have been used in watchmaking for hundreds of years. Mineral crystals are prone to scratching, and these scratches cannot be easily removed. They are less expensive compared to blue sapphire crystals. Subcategories within this category include:

Glass

In this type, a simple glass is used that is more resistant to scratches compared to its plastic counterparts. Usually, glass with a thickness of five to ten microns is used. It possesses the characteristics of ordinary glass and is resistant to color changes due to heat and the passage of time. These glasses maintain their transparency for a period of 5 to 10 years.
Application: This type of glass is used in inexpensive fake watches and grade 3 watches.

Hard Mineral

In this type of glass, standard glass is used that is resistant to scratches, color changes, and pressure through heat treatment and coatings. However, it is not ultimately considered scratch-resistant.
Application: It is mostly seen in branded watches and sometimes in grade two watches, which are replicas of the original watches.

Sapphire

The most desirable glass for watches is natural or synthetic blue sapphire. However, in the industry, synthetic sapphire is mostly used. Synthetic sapphire is made from crystallized aluminum oxide, which has the same physical properties as natural sapphire. It is also colorless, making it suitable for use as watch glass.

Blue sapphire has a hardness of 9 on the Mohs scale (a relative scale for measuring mineral hardness) and is slightly lower in hardness compared to diamonds, which have a hardness of 10 on the Mohs scale. Sapphire crystal, among various types of glass, has the least tendency to break or scratch. In fact, one should be more concerned about the watch causing scratches on other objects. The best way to test and distinguish sapphire glass from other types of glass is to attempt to scratch it. A stainless steel knife can leave scratches on regular glass, except for sapphire.

Viewing sapphire watches

Anti-reflective coated (Antireflex)

This technology involves a thin layer of special materials with a refractive index between the watch glass and the air to reduce the amount of reflected light. Glasses equipped with this specific layer are commonly referred to as anti-reflective or AR (antireflex) coatings. The AR coating can be applied to both mineral glass and sapphire crystal. Due to the higher refractive index of sapphire crystal (1.8) compared to glass (1.47), sapphire watches may benefit more from this technology.

Some watch brands, such as Breitling, add this coating to both sides of the watch glass to maximize the anti-reflective effect. However, this increases the overall price of the watch. In general, the anti-reflective coating is usually applied to the inner side of sapphire glass (to preserve its scratch-resistant nature)

Viewing watches with anti-reflective coating