Glasses of wrist watches: plastic, mineral, sapphire - advantages and disadvantages.

One of the important parameters that affect the choice of wristwatches is the properties of the glass installed in them. It is responsible for the aesthetic appearance of the model, and for the readability of the dial, and for protection from external damage. Further we will consider different types of wristwatch glass, their differences and main characteristics. What watch glass is made of Initially, personal watches, not yet wrist watches, but pocket watches, were equipped with glasses made of rock crystal. The finest work, exclusively handmade, high cost and small runs.... Of course, today it is in the distant past. There are three main categories of watch glass: plastic, mineral and sapphire.


Types of watch glass: acrylic, mineral or sapphire glass

Acrylic glass, organic glass, chrysolite glass, plexiglas (plexiglas) - all these are names of plastic glasses, which are made of thermoplastic resin. Their main features are lightness, high strength and inexpensive price. By the way, the common household word "Plexiglas" came from the brand name of such glass, Plexiglas, created in Germany in the 1930s. Plexiglas turned out to be incredibly popular in aviation of that time, namely in the design of the pilot's cabin lantern. Transparency, shatterproofness, simplicity of giving the desired shape: all these are the undoubted advantages of acrylic glass, which is still used today in many places, including ophthalmology and nanoelectronics. In the watch industry too, of course!

Plexiglas is lightweight, impact-resistant, easy to shape, polishable, easy to produce and inexpensive. Even brands such as Rolex used plastic glass in their watches 40-50 years ago. To this day, acrylic is still widely used in the budget segment and in sports watches.

Plastic glasses are elastic and therefore easy to produce: they can be shaped to any desired shape. As a result, they were widely used in watchmaking in the second half of the 20th century.
Acrylic glasses are also used by modern manufacturers, mainly for budget watches and sports models. They are also used for retro-style watches: the flexibility of the material allows watchmakers to easily create a convex glass with a pleasant distortion.

Advantages of acrylic glass

• Shatterproof - due to its flexibility, acrylic glass is virtually impossible to break. In the event of an impact, the watch face and hands will remain intact, because such glass does not break, but cracks.
• Minimal reflection - acrylic glass practically does not reflect light, so the watch face is perfectly readable even in bright sunlight.
• Possibility of polishing - watches with acrylic glass can be easily polished, which allows you to get rid of shallow scratches. On average, one such glass can withstand 3-4 polishings without loss of geometry.
• Low price - due to cheap mass production, replacement of acrylic glass, if necessary, will cost inexpensively.

Disadvantages of acrylic glass

• Exposure to scratches - when the watch comes into contact with different surfaces, small scratches remain on the acrylic glass. Over time, they can impair the visibility of the dial.
• Possible clouding and yellowing - acrylic glass may yellow over time, even if it has not been exposed to harsh environments. Due to multiple scratches, clouding is possible, and these problems unfortunately cannot be solved by polishing.
• Durability - due to its exposure to external factors (scratches, dust, sand) acrylic glass wears out rather quickly.

Mineral glasses are made from quartz sand with the addition of synthetic silicon oxide, which makes them stronger and clearer. They have similar properties to window panes.

It is currently the most common type of watch glass and is used mainly for mid-range models. Mineral glass is also used for the transparent back cover of skeleton watches, which allows you to observe the work of the mechanism.

Mineral glass is more resistant to scratches and shocks than acrylic glass. But it can still crack or break. Of course, mineral glass is more expensive than plastic, but more resistant to scratches. However, it is easier to break - this is the downside of hardness, which in mineral glass is 6.5 points on the Mohs scale (remember, the maximum belongs to diamond - 10 points). And it is not so difficult to scratch mineral glass after all

Watch manufacturers make different modifications of mineral glass with improved properties. Here are some of them:

• Hardlex - hardened mineral glass of increased strength, a development of Seiko company
• Flame Fusion Crystal - special hardened mineral glass from Invicta watch brand.
• Crystex - high-strength glass from Austrian watch brand Jacques Lemans.
• Gorilla Glass is a product of Corning. Chemically tempered glass that is resistant to impact and mechanical effects. It is used in the manufacture of displays for smartwatches.

Advantages of mineral glasses

• Aesthetic appeal - mineral glass looks more noble than acrylic and can be difficult to distinguish even from sapphire.
• Scratch resistance - mineral glass is strong enough that minor impacts on rough surfaces will not leave scratches. It is more scratch resistant than acrylic.
• Affordable price - mineral glass is more expensive to produce than acrylic glass, but cheaper than sapphire glass.

Disadvantages of mineral glasses

• Cannot be repaired - in case of damage (deep scratches or chips), as a rule, it is necessary to replace the crystal.
• Glare - most types of mineral glass glare in bright light.

Sapphire crystal is the highest level of this wristwatch component. It is related to the precious stone sapphire because it is also a crystalline aluminum oxide (Al2O3), one of the varieties of corundum. And it is distinguished by its artificial origin - first synthesized by the French chemist Auguste Verneuil in 1904 - and its complete transparency. In terms of structure, it is a single crystal obtained by melting aluminum oxide in the flame of a hydrogen-oxygen burner and the subsequent precipitation of droplets, which, cooling down, and form a crystal.

Synthetic sapphires are cut into thin (of the required thickness) sheets - this is the finished sapphire glass, or rather, blanks, from which glass for watches and other devices is then made. Sapphire is very hard, second only to diamond (9 on the Mohs scale versus 10), so it is cut with diamond tools.

Another feature of sapphire glasses is their perfect transparency. To avoid glare in bright light, they are coated with a special coating. The glass is treated with a compound that forms a thin film. This reduces light reflection and increases the contrast of the dial.

Due to their outstanding durability and transparency, sapphire crystal is considered to be the best type and is used in premium watches. Such watches are not suitable for aggressive sports: sapphire crystal may shatter in the event of a strong impact.

To utilize the best properties of sapphire, brands create combined types of glasses: mineral and sapphire. Some of the most popular developments include:

• Sapflex - mineral glass with sapphire coating developed by Seiko. It is scratch-resistant and has a smooth surface with water-repellent properties.
• Krysterna is a watch crystal developed by Stuhrling. It combines the scratch resistance of sapphire crystal with the mechanical strength of mineral glass.

Advantages of sapphire crystal

• Aesthetics - thanks to their exceptional transparency, sapphire crystal glasses guarantee improved readability of the dial. If an anti-reflective coating is applied to the watch, it can practically make this crystal "disappear".
• Reliability - sapphire crystal cannot be scratched in everyday use, so the watch will last for many years and look like new.

Disadvantages of sapphire crystal

• Low impact resistance It has the lowest impact resistance of all three types of watch glass. To be fair, it should be added that the difference in fragility compared to mineral glass is not so catastrophic, and in waterproof watches (where the glass is thicker) and does not manifest itself at all.
• High price - due to the high complexity of production and processing of the material.

The properties of watch glasses are influenced not only by the material from which they are made, but also by their shape.

Flat glasses are characterized by their simple production and installation. For example, this variant is used in Casio G-Shock watches. They are perfect for sports models, as they meet the requirements of practicality and fit perfectly into the brutal design.

Flat glass
Flat glass is easier to replace when needed. Their durability depends solely on the material from which they are made.
Convex glass protects the dial better than flat glass due to its thickness. This is why they are often used in professional diving models, so that the glass can withstand the pressure of the water.

Convex glass
The arc-shaped shape creates a lens effect, slightly magnifying the image on the dial. Spherical glass is often used in classic watches to create a smooth transition from case to glass and to keep the lines concise. Also, convex glass has a different glare, and many people like the readability of a dial with convex glass.
It should be noted that if the convex crystal is thin and rises above the watch case, the chances of breaking it are higher. It is also not always possible to replace a convex crystal in a servais, as they are rarer and the right size may not be available. Flat glass is usually much easier to replace.





Read our other article: How to determine for yourself what a watch crystal is made of