What is watch crystal? What is dial window? Can they get scratched or break? Can watch owners repair or replace them? These are some of the questions that anyone wanting to buy or already own a watch will surely have in mind – regardless of automatic, mechanical or quartz watch. Here I will cover all of these questions.
What Is Watch Crystal or Dial Window?
A watch crystal (aka dial window) is the glass in front of a watch and is as important as the case to protect the internal mechanism inside. As we use our watch to go to many places, it is the watch face that is most exposed to dirt, rain, water, or even impact from sharp edges. This is the job of the watch crystal – to protect the actual watch face (or dial) from these threats. Because of this, the crystals need to be strong and durable for it to be effective. It also needs to be clear so that we can still look at the watch to tell time. And lastly, it has to be secured to the watch itself to provide any water resistance rating needed.
Watch Crystal Types
There are typically 3 types of common watch crystals used in watchmaking.
1 – Acrylic Crystal
Acrylic is basically a type of plastic but not the soft easy to torn of kind of plastic. It is a special kind of plastic with the scientific name of polymethyl methacrylate (PMMA). A result of the chemical reaction gives a clear, durable and tough plastic which looks more like a glass due to its transparency. It has wide usage in our life today from kitchenware to lab equipment even to decorative items.
A typical decoration encased in an acrylic block
Acrylic is the among the first material to be used for watch crystals, which is why if you bought a vintage watch, then most probably it has acrylic crystal. Plexiglas and hesalite are some of the trade names for acrylic that is normally used for watchmaking.
Below are the characteristics of acrylic crystal:
- Very prone to scratch
- Very hard (does not shatter or break easily. It’s plastic after all)
- Looks different than other crystals (mineral and sapphire)
- Can be molded into shapes (very domed crystals)
- Warmer than normal glass crystal
- Will wear and have yellowish fog after some time
- Not as transparent as other crystals
- Can be polished
An Omega Speedmaster with Hesalite acrylic crystal. Notice how domed it is? That’s an added advantage of acrylic – it can be molded into various shapes
It might seem that acrylic is not a good material to be used right? Even though it is very easy to be scratched and will wear out with time, it has one big advantage compared to the other crystal types: it can be buffed out. By using polishing material such as Polywatch (more detail below) and Brasso, and some fine sand paper for deep scratches, an acrylic crystal can be made new in just minutes! That’s a very big advantage of acrylic crystal.
Another thing to note is commonly vintage watch has acrylic crystal for good reasons. First, that’s what is accessible at that time (other glass are just too expensive to be used in a watch). Second, acrylic can be shaped into domed crystals with very distinct and gives beautiful reflection under light. It will scratch easily of course, but these watch owners know that acrylic can be polished. Not to mention it also does not shatter like glass will, and have a higher impact resistance than other glasses. If you have a kid with a slippery hand, than this is the watch crystal you need to buy for your kids.
2- Mineral Crystal
Mineral crystal is basically glass that has been hardened by chemicals or heat treatment to make it more scratch resistant than normal glass and acrylic. It is also harder to break than normal glass (window glass, kitchenware, etc). Being a glass, the transparency it gives is also much better than acrylic and somewhat around sapphire quality. It is also very cheap, with most of affordable automatic watches using this crystal in their watch.
In terms of performance, mineral crystal is actually not that good. Sure it has a higher scratch resistant than acrylic, but it is still a glass, and glass shatters easily (more than acrylic/plastic). So it sits between the very scratch prone acrylic and the virtually not scratch-able sapphire crystal in scratch resistance, but bottom of the class in impact resistance. The only remedy for a scratched mineral crystal is by replacing it.
Above is Seiko SARB065 “Cocktail Time” with Hardlex crystal. Seiko loves to use it on many of their low to middle range watches
Knowing the issues with impact resistance of mineral, some watch companies have made their own proprietary mineral crystals with enhanced properties. Seiko has developed their own Hardlex crystal, which is basically a toughened mineral crystal. It has a higher scratch resistance and higher knock resistance than normal mineral (though not as good as sapphire).
A gorgeous blue sapphire ring gemstone. This baby can cost thousands of dollars while a synthetic sapphire crystal used in a watch can be had for a fraction of the price
3 – Sapphire crystal
Last but certainly not the least is sapphire crystal. Most of us knows that sapphire is a type of gemstone that can be in many colors (commonly blue) and is very expensive. Other than being pretty, sapphire also has a unique and desirable trait – it is very hard. It sits at 9 on the mohr hardness scale , below diamond (10) and another material called moissanite (9.5). This level of hardness means that it’s very scratch resistant. It’s also very transparent making it a great material for watchmaking.
But due to its very expensive price, naturally mined sapphire is not widely used until the invention of synthetic sapphire. By producing sapphire synthetically, the production cost is reduced by a lot, making it viable to be used for watch crystal. A lab made sapphire also has the advantage of being more clearer because it does not have impurities usually comes with mined sapphire.
A video showing how to synthetically make a sapphire glass in a factory. It’s truly fascinating how the advancement in technology have enables us to make our own gemstone!
The high scratch resistance of sapphire crystal makes it a very popular among watch lovers and it is being used in many middle to high end watches. You can own a sapphire crystal watch, use it everyday for years and at the end, it won’t even have any scratch marks on it. It is tougher than mineral but still not as tough to impact as acrylic. A very sharp impact (like dropping it onto the road filled with pebbles – but how can you be so careless like that?) can make a dent to the sapphire. Due to this, watch manufacturers usually give a special treatment to the glass or even thicken it to further toughen it up. One more thing to consider is it’s much more expensive than acrylic and mineral. So please treat your sapphire crystal watch carefully will ya?
A Tissot Le Locle with a Sapphire crystal. Most of Swiss brands use sapphire on their watches
And The Best Watch Crystal Material Is…
So what is the best watch crystal material? Mineral is the worst (not so scratch resistant as sapphire, cannot be buffed out, not so impact resistant like acrylic) but is the cheapest. Acrylic is highest in impact resistant, easily scratched but can be polished, and cheap. Sapphire on the other hand is very expensive but super scratch resistant and somewhat good in impact resistant (higher than mineral, but lower than acrylic).
In my opinion, sapphire crystal is the best for any watch. It’s high resistance to scratches means no heartache when you suddenly noticed a small hairline scratch on your watch. Sure, it’s not as impact resistant as acrylic but what are the odds of you breaking your watch glass? But all these comes with a higher price. But for that, you will get a highly scratch resistant dial window, that is also very transparent.
2 common problems with any watch crystal are scratches and breaks/cracks. Scratches are very common, not just on the dial window but also on the case and bracelet too. Acrylic is very easy to get scratches – just looking at them can give you one, while mineral is a bit better on this. Sapphire is highly resistant and will give you smooth crystals for years to come.
Watch crystals breaking is more uncommon and can happen to the most unfortunate guy (or if you are not careful with your watches). Acrylic is very hard to break, followed by sapphire and mineral. But another problem with acrylic is it can develop fogging which is typical with any plastic material.
Fortunately for acrylic watch owners, the crystal can still be repaired if it’s scratched or fogged. And it can be done at home, DIY by using polishing products. A very popular polishing products is Polywatch. It is more preferred over other products such as Brasso because it is specially designed for the fine acrylic crystal.
Just apply some of Polywatch onto the crystal and start giving it a circular massage with higher pressure on the scratched area. What will happen is the Polywatch substance will sand down some of the plastic and fill in the scratches. For very deep scratched, you might want to use sand paper first before using Polywatch.
But then will it thin down the crystal? Of course it will. But I won’t be too concerned about that because the thinning is very limited since we are using our hand to polished it. Polishing using machines is the real concern here because it can easily thin the crystal down. The end result is a clear flawless crystal. You can also use this to give life to vintage watches that have fogged acrylic crystal.
A video showing how to use Polywatch to polish and remove those scratches. It’s very cheap too (less than $10 a tube) and can be bought from Amazon. The most recommended way to remove those scratches for your acrylic (and is the cheapest way too)
Scratches on sapphire and mineral? Don’t bother with Polywatch as it can’t do a thing. The only way to deal with it is by replacing the crystal. There are some ways to polish a mineral or sapphire but these are not easy to do yourselves and will require machining which will thin down your crystal. In any case, it’s much better to replace it completely.
You need to be more careful with broken crystals. The broken shards from crystals (especially glasses – mineral and sapphire) is very small and can get inside the movement and blocking the movements of the gears inside. I would suggest to quickly stop the watch, and then throw the broken glasses off the watch. Be careful not to touch the hands or dial as these are sensitive. Throw off the glasses by flipping the watch upside down. Get a new replacement crystal as soon as possible, while protecting the uncovered watch in the meantime.
I hope you guys enjoy and have learned something from this article. It is important for all watch owners to know are the types of watch crystals and what are the characteristics so that he/she will know what to expect from it. And remember that you can easily polish the scratches off an acrylic crystal with just a $10 Polywatch tube and some discarded clothes instead of spending more to get it “professionally” polished or replaced at your local watch shop. Feel free to drop any comments below. Till next time.