High-End Apple Watches Use Sapphire Crystal Glass, original image from gearopen.com
As the window to your timepiece, the watch crystal takes some of the hardest hits, and the brunt of the everyday wear and tear. To extend the life of your watch crystal, crystals are made of different materials to ensure different kinds of strength. Plastic crystals are the most flexible of all the watch crystals, and therefore are used in a wide range of watches. Glass crystals are also common in watches.
The wonderful thing about plastic and glass crystals is the fact that they can be custom cut, shaped, or trimmed to fit different watch cases. Typically in the luxury watch field, sapphire crystals are preferred. Sapphire is extremely strong and scratch resistant – making it the top choice for a fine timepiece. There are three main types of crystals used in watches: sapphire, mineral and acrylic.
Acrylic is similar to plastic. It is light, durable and affordable type of crystal but prone to scratches. Acrylic crystal is mostly used for children watches, but not for fancy timepieces. Acrylic crystals have a unique advantage among other types of crystals: it can be polished to remove tiny scratches.
Acrylic Watch Glass, image from eurowatchglasses.co.uk
Flat Watch Crystal Lens Glass, image from images-amazon
Seiko SKX Original Hardlex Glass Crystal, image from media.karousell
Mineral crystal, also known as "Hardlex", is actually ordinary glass which has been heated and chemically treated to increase scratch and shatter resistance. Mineral crystals are quite durable but less durable than acrylic crystals.
NEW Seiko 5 SPORTS SRPD69K1 (FLAT HARDLEX CRYSTAL), Super-J Louis bracelet by MiLTAT
They will get some scratches eventually and they're not as easy to maintain as acrylic crystals. The cost for mineral crystal is quite cheap, so people would often replace the glass instead of having to worry about damaging the glass. Mineral crystals are mainly used on low-middle class watches.
Sapphire is the second hardest element after diamond so it is scratch and crack resistant, which can keep your watch look brand new despite constant use. To understand the hardness of sapphire, it measures at 9 on the Mohs scale, which is a system for rating the relative hardness of various materials, where diamond is rated at 10. Anti-reflective coatings can be added to both sides of the crystal without any hazing. While this crystal is called sapphire, it should be noted that it is not made from naturally mined sapphire.
2019 NEW Seiko Prospex Green Sumo SPB103J (Sapphire Crystal), Super-J Boyer bracelet by MiLTAT
A synthetic sapphire crystal or “glass” is actually not glass at all. It is a very hard, transparent material made of crystallizing pure aluminum oxide at very high temperatures. One of the reasons why sapphire crystals are relatively expensive is that the tools required to cut and polish this extremely hard material are very costly. Because of this, sapphire crystals are often used on high-end luxurious watches. Although sapphire crystals are often listed as scratch resistant, take note that its still possible to scratch the crystal. Diamonds, as well as man-made materials that contain silicon carbide can scratch the crystal.
Pros & Cons for the three common types of watch crystals
Easy to manufacture and manipulate to whatever shape desired
Inexpensive to produce; cheap to replace
Simple to re-polish
It won't shatter or break easily. When it does break, generally it will crack, but stay in place, -protecting the wristwatch's dial and movement from further damage
It scratches easily
Lots of scratches can impact visibility, and then will require the owner's efforts to either re-polish or replace the crystal
(Watch Models Used) New 2019 Seiko 5 Sports line-up of 27 models, SRP Turtles
Looks similar to sapphire at a fraction of the cost
Not as brittle as sapphire
It's much more scratch resistant than acrylic glass
Can be coated to increase scratch resistance
Less expensive replacement crystal when repairing watches
Superior scratch resistance. Only moissanite (9.25) and diamonds (10)exceed its hardness ranking (9) on the Mohs scale
Use of an Anti-reflective coating makes the crystal seem to disappear
Most expensive option
Prone to shattering due to its brittle nature
Difficult to polish
Three Anti-reflective coating on Sapphire Crystal, image from uhrforum.de/threads
The latest trend for modding SEIKO Diver watches or customising your Seiko DIY style, replacing the crystal seems getting more popular. To get the Seiko mods upgrade to the next level, sapphire crystal is the best option to be choose for it’s more reflective than mineral crystal due to its higher index of refraction. Applying one or more layers of AR (anti-reflective) coating will limit this reflection to a very low level, make the crystal seems like invisible.
How to Tell the Difference Between Watch Crystals
There are several ways to check what type of watch crystal you have on your watch, and its actually quite simple.
Acrylic Crystal - Clouded & abundance of scratch marks, produce a plastic-like sound when tap on the surface with your finger
Mineral Crystal - Clearer view than acrylic crystal, less scratch marks, product a high-pitch sound (sounds like tapping on glass), blue color, water will be divergent when drop on mineral glass
Sapphire Crystal - exceptional clarity, scratch free even against the likes of metal objects, easy to chip & shatter, water drop will flock together on sapphire crystal, pink/white color
Once you decide on the properties of watch crystal you prefer to use, you then have to decide on the design of the glass to go with. There are three types of watch crystals designs that are commonly used when it comes to selecting the shape/cutting of the watch crystal.
Flat - Flat on both sides, no magnification
Magnification cyclops added on the Date
Single Dome- Flat on bottom, curve on top, magnification factor, dial distortion
When it comes down to deciding on which design to use on your watch, it really depends on your personal preference. Some people may prefer the basic flat design, so they would not have to worry about banging or damaging the glass with wear and tear when worn on a regular basis. Some people may prefer to go with the single dome design, which enables magnification factor. However, some may be even willing to pay extra to go with the double dome design, simply because they like the looks of it.
Single Dome - domed top surface flat underside magnifies a little bit and the crystal distorts the dial at extreme angles.
Double Dome - round on the outside and inside which means it does not have any or just very little distortion when looking at the watch dial from an angle. It's more expensive to produce but I think they look a lot better.
Ways To Remove Scratch Marks On Watch Glass/Crystal
Identify the type of crystal on your watch
Select the appropriate polishing agent (different for each glass/crystal)
Contact manufacturer if uncertain of which crystal used on watch
Use painter’s tape to protect the watch to avoid damage during cleaning process
Apply a small amount of polish on the cracks and scratch marks on the crystal and rub it with a soft cloth for a few minutes
If the scratch mark is too deep and not removable, can use a stronger polish agent, or consider to replace the watch glass
Unavoidable scratches on your watch glass are bound to happen over time. However, with proper tools, and various polishing agents, (depends on type of crystal), and a few guide lines to look out for, minor scratch marks can be removed. If the scratch mark is too deep, and not removable even after buffing and polishing the crystal repeatedly, replacing a new crystal would be the only alternative option.
The three watch crystals mentioned above that are used often today remain incomplete, as each crystal have their strengths and weaknesses. While acrylic crystal can sustain the most damage among the three types of watch crystals, its downside results in clarity and scratch resistance. As for mineral crystal, although it is cost efficient, as well as heated and chemically treated to strengthen the crystal, they are not as durable as acrylic or sapphire crystal. Sapphire crystal will remain as the top choice when it comes to the selection of watch crystal because of its clarity, strength, and scratch resistance, which will allow your watch to remain in top condition for a very long time.
Written by Sam , photo by Toni & other sources as noted