In the watch world, watch crystal is a generic term for the transparent glass material that covers the watch face. It is like a transparent cover that protects parts of a watch such as watch dial, watch hand from dust, moisture and other natural disasters. The watch crystal on the market is not actually made of crystal, but a man-made material that resembles crystal. This blog aims to improve the watch collector’s overall understanding of watch crystals and how to replace a watch crystal.

Table of Contents

What is a watch crystal

    Watch crystal, also known as watch glass, refers to the clear glass material that covers the face or watch hand. Watches glass belong to watch case parts,protecting it from the elements and providing your watch with a polished look. Watch crystals are available in a variety of materials, each with their own unique properties and characteristics. Understanding what is a watch glass used for and the differences between these types is essential to choosing the right watch crystal for your watch.

what is a watch crystal

Watch crystal types

    There are 4 types of Watch glass, namely Acrylic crystal, plexiglass, Mineral crystal and Sapphire Crystal. Acrylic glass and Plexi glass are a kind of plastic, so they are cheaper, transparent and lighter. Most watch manufacturers use these four types of crystal watch, and we will introduce these four types of watch glass one by one.

Acrylic crystal

    Acrylic watch crystal is a polymer comprising a polymethyl methacrylate. In the days before sapphire crystal was so common, Acrylic glass was one of the most common watch glasses because it had impact and shock protection.
     Even if the acrylic glass takes a powerful hit, it will crack, but it will stay in place, protecting the dial and watch movement from further damage.
In the 1980s, even Rolex used acrylic glass. The reason it was replaced by sapphire glass is that acrylic glass is more prone to scratches or scuffs, as well as poor light transmission, and the watch can look a little hazy. Besides this, acrylic is less costly and is used on some vintage watches. Acrylic glass can withstand the pressure of a certain depth and is flexible, because some dive watch or military watch also use acrylic crystal glass. 

Acrylic crystal

Plexiglass

   Plexiglass is a polymethylmethacrylate (PMMA) plastic material that is harder than acrylic glass, has better impact resistance, and costs less than acrylic crystal.
Plexiglass transmittance is over 92% or more, and acrylic transmittance is around 85%. So plexiglass clarity is higher.
   But plexiglass is easy to scratch but there is easy to polish. We often use them in sports watches because of their impact resistance and lightweight.

Plexiglass

Sapphire crystal

   Sapphire crystal is a synthetic sapphire material. Most of the luxury watches in the watch industry are equipped with sapphire crystal because sapphire glass has the following advantages:
    1. Hardness: the hardness of sapphire glass is 9, which is only second to the hardness of mission and diamond.
    2. Difficult to scratch, wear-resistant
    3. High clarity and good light transmission, which is conducive to improving visual recognition and making it easier to read the time. So high-end watches are favored to use sapphire glass. Sometimes the glass of mechanical watches is made of sapphire crystal, even the back of the watch is crystal sapphire.

what is the crystal on a watch

    Sapphire glass is expensive because the hardness of sapphire glass is so high that it has to be cut and polished with diamond abrasives. This kind of abrasive is not only costly but also has a short service life, resulting in the high cost of crystal sapphire.

   In addition, although sapphire is wear-resistant, we will break it when it encounters heavy pressure, water, and heavy fall. Once broken, it is easy to scratch the watch face and hand. The cost of repair is high, and before replacing the Sapphire crystal glass, the watchmaker has to make sure that no sapphire fragments are left inside the movement and other watch accessories.

What is an analog watch Sapphire crystal

Mineral crystal

   Mineral crystal is also known as mineral glass, the key component is silicon dioxide. Mineral glass is the most common watch glass mainly used in some mid-range watches, has the following advantages:
Less fragile than sapphire glass
Lower cost

Resistant to heavy pressure, stronger impact resistance, able to withstand great depth and pressure. Therefore Mineral glass is used in some diving watches.
Reflects less light than sapphire
   However, the Mineral crystal watch is more prone to scratches than crystal sapphire glass and is more difficult to polish. But we can coat it to increase the scratch resistance. Mineral glass is usually coated with anti-reflective coating, which can help the wearer read the time in a poor light environment and reduce the burden on the eyes.

How to replace a watch crystal

     When your watch crystal is damaged or has too many scratches, replace it.

     Step 1: prepare the tools, including fresh glass, tools to pry open the glass and the back cover.

    Step 2: Remove the back of the watch case.

   Step 3: Remove the broken watch crystal and note if there is any glass debris falling inside the dial or movement.

     Step 4: Clean the inside of the case or bezel.

   Step 5: Install the fresh glass using the base, making sure that the glass is not higher than the case.

     Step 6: Reinstall the base back into the watch.

    Step 7: Perform a water resistance test to ensure that the watch is waterproof. If you don’t have a specialized instrument, you can put the watch in the water to see if water enters.

   Before replacing the watch crystal, please make sure you have enough experience and skills to avoid causing secondary damage to the watch. If you are not sure how to replace watch crystal, you can send it to a professional watch repair store for replacement.

Conclusion: What is a watch glass

   In short, the watch crystal plays a vital role in protecting the inner workings of the timepiece and clearly displaying the dial. By understanding the differences between mineral, crystal sapphire, acrylic crystal and Plexiglas crystals, watch enthusiasts can make an informed decision when choosing a replacement crystal. Plexiglass is the most resistant to knocks and bumps, and is even better suited for certain styles of watches, but lacks in clarity and scratch resistance. Acrylic glass is like plexiglass and by then more expensive. Mineral glass, with additional treatments such as coating, can be used as an alternative to sapphire at a fraction of the cost of sapphire glass, but lacks in scratch resistance. Most times, sapphire crystal is still the preferred choice for luxury brand watches because of the high clarity and scratch resistance of sapphire glass.

  As a China watch factory, Watchessy can provide different grade watch crystal to meet our customer’s request.

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