If you ask any experienced watch aficionado what’s the most integral part of a timepiece, he’s likely to point to the movement.
And, quite frankly, it would be hard to disagree.
However, because of the importance they play in protecting the mechanisms of timepieces, watch crystals aren’t far behind. Or at least they shouldn’t be when considering your next purchase.
In general, we differentiate between three main types of watch crystals: acrylic, mineral, and sapphire. And that’s the only information most websites for watch enthusiasts cover.
On Timepieceking, we will additionally discuss a cheaper alternative to sapphire crystal – sapphire-coated mineral glass. As well as this, we will have a look at brand-specific types of watch glass, such as the Hardlex crystal utilized by Seiko timepieces.
Without further ado, let’s go.
Definition of Watch Crystals
The see-through glass that covers the face of a watch is referred to as a watch crystal.
Its purpose is to protect your watch from the elements while also giving it a polished appearance. The majority of watch faces in the market are constructed of a variety of manufactured crystalline glass-like materials rather than a crystal. The vast majority of watchmakers use three types of glass: acrylic, mineral, and sapphire.
We’ll now discuss each type.
Three Different Types of Watch Crystal
As already mentioned, we differentiate between three main glass types utilized by watch brands all around the globe. Each is a characteristic of watches oscillating in different price baskets and made by watchmakers of varying status.
Let’s start with the least premium type and work our way up to the most sought-after (and costly) crystal.
Acrylic glass is also known under different acronyms, such as acrylic crystal, acrylic lens, plexiglass, or just plastic. Hence, many mistakenly think these are different types of glass with varying qualities. They’re not.
By some distance, it’s the cheapest of all types of watch crystals. It’s no surprise then that mostly the low-budget brands manufacture watches with this glass. The crystal is also popular in watch collections dedicated to children.
Because of the plastic substance, the crystal is much more flexible than the two other types. Hence, the watchmakers have pretty much free reign in terms of what shape they want the glass to be. For example, giving such crystal a domed effect is a walk in the park compared to trying to achieve the same feat with mineral or sapphire glass.
The acrylic glass was widely used and accepted up until the 1980s. However, in today’s market that is flooded with mineral and sapphire crystal watches, it’s pretty much frowned upon.
A fun fact: it wasn’t until 1979 that brands like Rolex ditched the acrylic glass. Just over four decades ago, arguably the most-renowned watchmaker in the world was using the same type of glass as today’s watches for kids.
Apart from being cheap and flexible, acrylic is also very light. However, its biggest drawback is the proneness to scratches and cracks. On the bright side, it’s by far the easiest to buff out.
Mineral crystal, also known as mineral glass, is by far the most frequently used glass type in today’s market.
Not many people are aware that mineral glass used in timepieces is exactly the same type of material that’s used with windows. Because of the commonness, the glass is considerably cheaper to source and manufacture than sapphire which we will discuss in a minute.
Without a doubt, mineral crystal glass is much more durable than acrylic. It ranks 5 out of 10 on the Mohs hardness scale. Prior to getting installed in timepieces, it’s hardened by heat and additionally coated with a hardening mineral. That’s the exact process that makes mineral crystal vastly superior to acrylic in terms of scratch and impact resistance.
With that said, mineral glass is not unbreakable by any means and under extreme conditions (hot or cold), it may crack or shatter.
Unlike the sapphire.
The last of the three main types of watch crystals, and by far the most desirable.
Also referred to as sapphire crystal, it’s without a doubt the most scratch and crack-resistant glass used in watches today. The glass is a must-have element of all premium timepieces such as Rolex, Tudor or Patek Philippe.
With that said, just because you are not willing to spend a 5-figure sum on a wristwatch, doesn’t mean you can’t experience the robustness of sapphire. As proved in our list of top sapphire glass watches under $300, these timepieces are possible to acquire at affordable price points.
Sapphire crystal glass scores 4 points more on the Mohs scale than mineral crystal glass (9 out of 10). That makes the substance the second hardest on the planet Earth, with diamond placed at the very top of the list. Such a high score makes sapphire crystal glass near impossible to scratch, with only the leading diamond really capable of causing visible damage.
What’s worth noting, not all watchmakers use natural sapphire crystal glass in their products. A large part of the industry, especially the brands operating in the mid-price range, use synthetic sapphire which is constructed of crystallized aluminum oxide.
Despite being the toughest and most reliable type of watch glass, sapphire isn’t unbreakable. Extremely heavy impact, ie. dropping a gym weight, might lead to shattering. Also, it requires extremely delicate and careful work during the milling and cutting processes.
What’s worth noting, many watch brands that use sapphire crystals in their watches enrich it with an anti-reflective coating. This makes the time-telling extremely comfortable in any light. The transparency is so good you might actually forget at times that the crystal is even there!
Cheaper Alternative: Sapphire-Coated Mineral Glass
Also referred to as sapphire-coated mineral crystal, this type of material is the freshest addition to the watchmaking industry.
The last decade or so has seen a notable increase in the number of watchmakers utilizing this glass type, mostly amongst the brands in the med-priced sector and microbrands, such as Torgoen, AVI-8, or Reign. Also, a much more recognized brand in the form of Seiko used the material, albeit under a different name – Sapphlex.
During the last few years, however, the “wow” effect of sapphire-coated mineral crystal has worn off as the cost of sourcing natural sapphire crystal continues to drop.
Sapphire-coated mineral crystal is effectively a mineral glass for the most part with an additional coating of sapphire crystal applied to it.
On the durability front, the material is probably somewhere between regular mineral and sapphire crystals. It’s not unusual for the glass to be advertised as combining the best elements of both glass types. With that said, some aficionados report the sapphire layer chipping off in time from the mineral glass.
Brand-Specific Types of Glass
As already mentioned at the beginning of the article, some brands utilize their own forms of glass.
If you’re familiar with watchmakers such as Seiko or Stuhrling, the chances are that you’ve come across unique-sounding names that made you wonder: how reliable are those?
In this section, we will have a brief look at the most popular alt-names for the main types of watch crystals covered above.
Simply explained, a Hardlex crystal is a Seiko-exclusive watch crystal used in several of their timepieces. The Hardlex crystal may or may not include an anti-reflective (AR) coating, depending on the model.
In order to create the Hardlex crystal, Seiko heats and chemical treats ordinary glass. The mineral’s resistance to scratches and shatters is improved as a result of these adjustments. Hence, the Hardlex crystal is considered more robust than regular mineral glass. The material is typically found in Seiko’s entry-level timepieces, such as the Seiko 5 series (read also: Top Seiko 5 Watches).
This type of glass is another attributed to Seiko.
The Sapphlex crystal was particularly popular in Seiko timepieces during the 90s and the early 2000s. Once the price of regular sapphire started dropping, Seiko decided to decrease the number of new releases utilizing the glass before completely stopping the production. However, it’s still possible to come across it online when shopping for pre-owned Seiko models from 2-3 decades ago.
Despite its production being discontinued, Sapphlex crystal was a popular choice amongst people looking for extreme robustness at competitive prices. The glass combined the outstanding scratch resistance of sapphire crystal with the shatter resistance of a Hardlex glass.
Another alternative crystal type you might come across is Krysterna. It’s a proprietary glass produced and widely used by the American watchmaker, Stuhrling. The material isn’t exclusive to Stührling watches but is also used with another watchmaker owned by Stuhrling, Akribos.
To achieve clarity and durability, it was created in collaboration with the eyeglass industry. According to Stuhrling, Krysterna is more shatter-resistant than sapphire crystal but doesn’t provide as good protection against scratches. Its biggest selling point is the great legibility and transparency, often compared to the anti-reflective coating used with other crystal types.
Types of Watch Crystal: FAQ
To round off today’s article, below we’ve collected some of the most popular questions on the subject. If there’s anything missing, make sure to let us know in the comment section at the bottom of the page.
Mineral Crystal vs. Acrylic: How To Differentiate?
If you’re shopping on a budget, you’re likely to come across watches with either acrylic or mineral glass.
Folks who prefer to do their shopping in physical stores should be easily able to tell the difference between the two glass types simply by rubbing their finger across the crystal’s surface.
Before starting the test, make sure the glass is clean. Next, press the finger against the surface and then move it side to side. Hearing any whiny noise indicates the watch has an acrylic crystal.
On the other hand, a lack of noise during the test means the watch is utilizing mineral crystal (or sapphire).
Mineral Crystal vs. Sapphire Glass: How To Differentiate?
Another instance in which a simple test can help you determine the glass type is when you’re shopping in the mid-price category that’s full of both mineral and sapphire crystal watch models.
Bear in mind that this test might be a bit risky to do in a physical watch store!
To perform the test, put a few drops of water on the crystal and see what happens.
If the watch has sapphire glass, the water will slide off and at most will have a couple of small drops stuck to it.
In the case of mineral glass, most water will stick and spread throughout the surface.
What Is the Cheapest Watch Crystal Type?
The cheapest type of watch glass, both in terms of the production costs and the quality, is acrylic glass.
Although it was widely used even by the best of the industry up until the 1980s, nowadays you can find it mostly in Chinese watch brands or kids watches.
What Is the Toughest Watch Crystal Type?
By some distance, the hardest-to-scratch and most robust glass type is sapphire. It’s rated 9 out of 10 on the Mohs hardness scale. It’s 4 points more than the second-hardest material used in watches, mineral crystal.
Which Crystal Is Used to Make Modern Watches?
If we were to pick one glass type that’s most commonly used across all collections of all watch brands in the market, it would have to be mineral crystal.
Mineral glass is much stronger than acrylic but some way off the hardness of sapphire crystal which is generally used by high-end watchmakers.
The use of acrylic glass in watches is decreasing year on year.
How Do I Make My Watch Scratch-Resistant?
You can improve the scratch resistance of your timepiece by additionally getting a plastic screen protector for your crystal. It’s very much in the mold of the one you normally purchase for your mobile phones.
All you have to do is get the product for peanuts online, then peel off the back of the plastic and apply it to the dial window.
How Do I Remove Scratches From My Watch Face?
While it’s not easy to completely get rid of scratches on a watch glass, it’s not impossible.
The whole process takes just a few steps.
For mineral and sapphire glass, do the following:
- Use some form of masking tape to cover the bezel of the watch
- Apply a small amount of 3µ diamond paste to the surface with scratches. Let it sit for around 60 seconds
- Using a polishing cloth, rub the paste hard in a circular motion for several minutes or until the scratch disappears
- Apply a small dab of .25µ paste to the face of your watch, and, using the clean part of your polish cloth, work it in a circular motion
- Wipe away any extra paste with a clean part of your cloth, then remove the masking tape after the scratch is totally gone and you’re happy with the results. Repeat Steps 2–4 if the scratch is still visible
For watches with an acrylic lens, try:
- Apply a small amount of standard non-gel toothpaste to the affected surface of the watch face
- Using a clean polishing cloth, work the toothpaste in a circular motion
- Use a paper towel to wipe the watch face clean. If you notice the scratches are still there, reapply the toothpaste, flatten it into the damaged surface and let it sit for extra 5 minutes
- Apply mild pressure to the paste and work it in a circular motion once more
- Using the same circular motion, buff the watch face with a clean section of the towel, cleaning away all of the toothpaste
Do Rolex Watch Faces Scratch?
Many folks come to the conclusion that because Rolex watches are so expensive, they’re unbreakable.
Far from the truth.
Despite the well-earned reputability, Rolex timepieces use the same form of sapphire crystal glass as anyone else. And as we’ve already explained, despite the amazing toughness, sapphire is also prone to damage. Therefore, Rolex watch faces can scratch, too!