Mineral vs Acrylic vs Sapphire: The Guide to Watch Crystal Materials

Watch crystals are an important component of a timepiece, protecting the watch face from damage, while also adding to the look and feel of the watch. Watch crystals come in a myriad of shapes and sizes, and using different materials can change the characteristics of a watch.

In this article, we will explore the history, characteristics, pros, and cons of different watch crystal materials commonly found in affordable watches under $1500.

The History Of Watch Crystals

The history of watch crystals dates back to the 17th century, when “rock crystal”, a form of quartz, was introduced into watchmaking.

In the 19th and 20th centuries, new materials such as synthetic sapphire and acrylic were introduced into the craft. The introduction of acrylic glass in the 1930s, also known as hesalite, marked a significant innovation in the field, being exclusive and limited to only the most luxurious watches. Hesalite crystals were used by Panerai for its Radiomir watch models, designed for divers in the Italian Navy, and Omega also used this material for its iconic Speedmaster watch, which was eventually worn by astronauts to the moon.

In the 1970s, a process of strengthening mineral glass in a salt bath was introduced, making it a viable and cost-effective option for watchmakers. These days, the majority of watch crystals are either mineral, acrylic or synthetic sapphire.

Factors to Consider When Choosing Watch Crystal Materials

Scratch Resistance: How well does the crystal resist everyday wear and tear, particularly from bumps and brushes against hard surfaces?

Clarity: Does the crystal offer clear views of the watch face, ensuring optimal readability and appreciation of the watch’s intricate details?

Durability: Can the crystal withstand accidental bumps, drops, and potential impacts without succumbing to cracks or shattering?

Weight: Does the crystal’s material add significant weight to the watch, affecting its overall comfort and wearability?

Cost: How does the crystal material impact the overall price of the watch? Balancing affordability with desired features is crucial for budget-conscious watch enthusiasts.

Common Watch Crystals Materials: Mineral vs Acrylic vs Sapphire

We have a summary of the differences between mineral, acrylic and sapphire crystals in the illustration below:

Now let’s explore each material in more details:

1. Mineral Glass: The Classic Choice

Due to its affordability and ease of production, mineral watch crystals are the most common type found in watches, typically seen in mid-range to entry-level watches.

They are made from ordinary glass similar to that used for windows, and treated to prevent splintering in the event of breakage. Almost all mineral crystals are now “tempered”, strengthening them and making them more scratch-resistant.

Mineral glass is often used in conjunction with other materials; for example, Seiko’s “Sapphlex” crystals are mineral glass with a layer of synthetic sapphire.

Mineral crystals are hard-wearing, relatively inexpensive, and can be coated with an anti-reflective layer to improve visibility. However, they are still prone to scratches and chips, and once damaged, they cannot be repaired, requiring replacement.

To enhance mineral crystal’s scratch resistance and durability, another variation of regular mineral crystal undergoes additional treatment to create hardened mineral crystal. Hardlex,  a proprietary formula developed by Seiko, is a type of such hardened mineral glass used in their non-luxury watches.

2. Acrylic Crystal: The Affordable Choice with a Rich History

Acrylic crystals, also known by brand names like Hesalite, Plexiglass, and Perspex, are a common feature of vintage watches. In the past, Rolex used acrylic crystals up until the 1990s. Now, they are still present in most low-cost timepieces.

Acrylic glass has a thermosetting quality, meaning it can be heated and moulded into shape. It is also relatively inexpensive to produce and replace.

One of the main advantages of acrylic is that scratches can easily be buffed out, or polished with an inexpensive polishing compound. The flexibility of acrylic can also work to accommodate impacts, instead cracking but staying together, and acrylic is more shatter-resistant than many other materials.

However, acrylic is susceptible to scratches, and has a lower perceived value than other materials.

3. Sapphire Crystal: The Pinnacle of Clarity and Strength

Sapphire watch crystals, on the other hand, are the most expensive option, and are found mostly in middle to high end watches.

They are not actually made of glass but are synthetic sapphire, produced by crystallising pure aluminium oxide at very high temperatures. This process creates a very hard, scratch-resistant material. Sapphire crystals are often marketed as “scratch-resistant”, and while this is generally true, they can still be damaged if subjected to sufficient force; diamond is one of the few substances that can scratch them.

Sapphire crystals require special tools to be fitted and, once damaged, they cannot be polished or repaired and need to be replaced. They are also more reflective than mineral crystals, which can reduce visibility. However, this can be counteracted with an anti-reflective coating.

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