Sapphire crystal VS mineral, what is the difference?

When buying a watch, we recommend considering the type of glass used: mineral or sapphire. Watches with mineral glass are generally cheaper, but this type of glass is susceptible to damage. Sapphire crystal, on the other hand, doesn't scratch, but it is much more reflective. So, which watch glass should you choose? In this article, we describe all types of watch glass and the advantages and disadvantages of mineral versus sapphire crystal, so you can make the right choice. 

The different types of watch crystal

Mineral and sapphire crystal aren't the only materials used for watches. Another commonly used material is acrylic (plexiglass). 

Plexiglass 

Plexi was widely used in watches up until the 1970s because it is strong, flexible, and can be pressed into all sorts of shapes. It doesn't break, but it is very susceptible to scratching and tarnishing. 
Fortunately, plexi can be easily polished by a watchmaker. Or you can polish plexiglass yourself with Polywatch polish. 

Today, Plexiglas is primarily used in plastic watches like Swatch. Plexiglas is also regularly used in reissues of classic watches for a true retro feel.

Mineral crystal

Mineral glass is made of silica glass that has been chemically treated or tempered to make it stronger. Mineral glass is clear, relatively inexpensive, and easy to work with. That is why, it remains the standard choice for watch glass. However, mineral glass is susceptible to scratches and can break. But don't worry, you'd have to hit the glass really hard for it to break!

Coated mineral crystal

Some watch brands apply a coating to their mineral glass to make it more scratch-resistant or anti-reflective. A well-known example of coated mineral crystal is Seiko's patented Hardlex. Like sapphire crystal, Hardlex can be made in various shapes, both flat and domed.

Gorilla Glass 

Gorilla Glass is a brand of hardened mineral glass used mainly in smartwatches and sports watches. It is primarily used as a cover to protect the touchscreens of wearables. 

Sapphire crystal

One of the first times sapphire crystal was used in a watch was in the Rolex Datejust in the early 1970s. For a long time, sapphire glass was the go-to glass for luxury watch brands. Sapphire glass is rock-hard—just below the value of diamonds—and therefore almost never scratches. It is very clear and can be cut into all sorts of shapes, for example, with a date cyclops incorporated into the glass. 
Sapphire crystal is considerably more expensive than mineral. Nevertheless, nowadays, brands in the lower and mid-range segments are increasingly opting for sapphire crystal due to its superior quality.

Advantages of sapphire over mineral crystal

The major advantage of sapphire crystal is that it is virtually scratch-resistant and tarnish-resistant. It is made of synthetic sapphire, which consists of aluminum oxide fused at a high temperature. This material is cut into thicker disks that can then be cut into any desired shape. Because the material is so dense, it can withstand extremely high and low temperatures and even most corrosive chemicals. 
Sapphire crystal is also extremely clear, ensuring clear visibility of the dial.

Disadvantages of sapphire crystal 

Although sapphire crystal is incredibly hard, it is also relatively brittle. Sapphire crystal won't scratch easily, but a fall on a hard surface or impact at an angle against a sharp object can cause it to crack or shatter. In that case, unfortunately, the only option is to replace the crystal. 

Sapphire crystal is also a very stiff material, making it less suitable for use in watches intended for deep-sea diving. Plexi or mineral crystal are often used for this purpose because these materials are more flexible and bend with pressure variations.

Another disadvantage of sapphire crystal is that, due to its high clarity, it reflects more than mineral glass. That is why sapphire crystal is often treated with an anti-reflective coating (AR). With such a coating, it sometimes seems as if there's no glass in the watch at all!

Why is sapphire crystal more expensive than mineral crystal? 

The production of sapphire crystal, which involves melting and crystallizing aluminum oxide at very high temperatures, is more expensive than that of mineral glass. Furthermore, due to its hardness, processing the material is more difficult and labour-intensive than with mineral glass, which translates into a higher price.

How can you tell if a watch has a sapphire crystal? 

All the watches we sell list the type of crystal in their specifications. If a watch has a sapphire crystal, this is often also indicated on the dial or case back of the watch. 

If you don't know which crystal a watch has, you can determine whether it's sapphire or mineral crystal using a few simple criteria. It's helpful to have another watch that you know has mineral crystal handy for comparison. 

First, perform the water droplet test: Carefully drop a small drop of water onto the watch crystal. Sapphire crystal has high surface tension, causing the water to "roll" off like a droplet. If the water spreads out flat across the surface, it's probably mineral crystal. 
Also, look at the edge of the crystal. Sapphire crystal is usually colourless or has a slightly pinkish tint. Mineral crystal tends to have a greenish or blue tint. 
Finally, feel the crystal. Sapphire glass feels slightly cooler than mineral glass.

Shop watches with a sapphire crystal at Watch.co.uk 

Browse our collection of watches with a sapphire crystal for men and women and be amazed by the diversity!