If you are a Seiko fan, you may know that the Japanese watch brand uses a proprietary mineral crystal called Hardlex in many of its models. It’s not difficult to find a mid-tier Seiko watch that features a Hardlex crystal, and most of the entry models use it. 

Seiko has been using Hardlex since 1970 and registered the trademark for the name in 1980. 


Source: The Slender Wrist


Similar to other standard mineral glass crystals, Seiko makes Hardlex crystal using ordinary glass, and heat treats to improve its scratch and shatter resistance. Hardlex also has the extra advantage of adding inorganic chemicals to the surface.

Although Hardlex is a step above regular mineral crystals in hardness and is the middle-ground between super-premium sapphire and affordable mineral crystals in terms of scratch-resistance, it’s just not competitive against sapphire crystal.

Watch enthusiasts usually swap the OEM crystal of the much-loved Seiko SKX007 with a sapphire crystal as one of their first few mods. Keep reading to learn why!

What Are Sapphire Crystals?

As the main function of a watch crystal is to protect the movement and dial of a timepiece, it’s important to choose a watch crystal suitable for your lifestyle. 

Normally, strength and scratch resistance is what make a watch crystal premium, especially when your casual watches are subjected to high-impact activities.

Synthetic sapphire is brilliant, highly transparent, and the most scratch-resistant, which is also its most outstanding feature. In addition, it’s often treated with an anti-reflective (AR) coating for extra clarity when viewing the watch dial in any angle.



Produced in a lab, synthetic sapphire is made of pure aluminum oxide (Al2O3) that is technically not glass at all but a transparent mineral. It is considered one of the hardest substances on earth. 

Mineral hardness is measured using the Mohs scale, and sapphire scores a 9 out of 10, surpassed only by moissanite and diamonds. 

In fact, manufacturers can only cut sapphire by diamond-coated saws, this is also one of the reasons why sapphire crystals are relatively expensive. You can see that the tools required to cut and polish this extremely hard material are very costly.


Source: Bob's Watches


In the watch industry, Sapphire has been used since the 1930s and became common in the 1970s when Rolex built their ref. 5100 with a sapphire crystal.

Since then, watch sapphire crystals also became a choice for high-end brands like Patek and Vacheron, as well as the Grand Seiko line. Some luxury watchmakers even have created proprietary sapphires, like Rolex’s green Milgauss crystal.

Pros and Cons of Sapphire Crystals

There are 3 main types of watch crystals, Plastic, Mineral, and Sapphire. Plastic ‘glass’ used to be the norm. It is mainly used in inexpensive watches or for watch crystals with a very high degree of curvature. 

However, its main disadvantage is that it is highly sensitive to scratching. Plastic crystals are the least scratch-resistant, least clear, and weakest option on the list.

Meanwhile, Mineral crystals are the original dial protectors of the watch world. Today, these are common on most mid-range watches. Although they are a little more expensive than plastic crystals, they are significantly more scratch-resistant.



When comparing a watch crystal with other main types of watch glasses – Minerals like Seiko Hardlex and Plastic, sapphire crystal is excellent for resistance to scratches. If you are looking for clarity and an unmatched scratch-resistance, a premium sapphire crystal is a way to go.

However, sapphire isn’t perfect. 

First of all, it requires higher outlay than other kinds of watch crystals. Sapphire crystals are produced using a very complicated technical process and the raw material is extremely laborious to work with, as the material can only be cut by diamond tools.



Not only that, achieving the final high-gloss polish that is essential for the optical quality of the glass can only be done with diamond-based grinding pastes, and this is a very time-consuming process.

Moreover, Sapphire has a very high refractive index and high reflectance, therefore, AR coatings are a necessity to reduce annoying reflections that are added on wristwatches in everyday use. This wafer-thin layer will ensure a clear and unrestricted view of the watch dial, but it comes at a price. 

Normally, lines and marks on the top surface of a sapphire crystal are mistaken for scratches but are actually the scratched AR coating, or just AR coating wearing off over time. 



However, if you scratch a sapphire crystal, the damage cannot be polished away and will need to be replaced.

As sapphire crystals are extremely hard, they have little or no flex, therefore, when the crystal is inserted into a hard, steel, or titanium watch case, it will require a gasket to ensure a waterproof seal. 

Over time, these crystal gaskets can become brittle and break, so you will need to change the crystal gaskets every few years to ensure the waterproof performance of your watch.

Is it Worth Paying For A Sapphire Crystal?

The good news is that if you want to upgrade your watch crystal, you don’t need much. We have a range of SKX007 crystals, and lenses for other models too. 

All you need is a new crystal, and a matching gasket! 

Strength and scratch-resistance are what make a watch crystal premium. If you buy a luxury watch, it'll have a sapphire crystal. Otherwise, you might want to upgrade to a sapphire crystal on a vintage piece as well.

You can also upgrade mid-tier watches, budget watches, and affordable automatic watches with a new sapphire crystal, and other watch spare parts for a subtle but noticeable upgrade. 



As the window to your timepiece, a watch crystal often takes some hits during daily activities, which will lead to wear and tear. You might want to consider a new sapphire crystal, and we have lots for you to choose from here at namokiMODS.

Anyone who knows Seiko mods knows that the Watch crystal on a SKX007 mod is one of the first parts to get swapped for an aftermarket sapphire lens. 

If you want to use some of the best Watch mod parts out there, check out our online catalog, and also look at the new OEM Seiko spare parts we offer. 

You can upgrade an old Seiko, or start with all new parts, and build a watch you love. 

Happy modding! 

September 20, 2022 — Jeremiah A

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