Whilst many watches use a quartz crystal oscillator to control their movement, the crystal of a watch actually refers to the glass that is used to protect the watch dial from dirt and water. There are three main types of crystal used in horology; sapphire, mineral, and acrylic. The glass, or crystal, is probably one of the first things you notice about a watch, and is the first point of contact between your watch and any bumps, so it pays to know about what exactly yours is made out of. Read on the find out more:
Often synthesised in a laboratory for the specific application of use in watches, synthesised sapphire has exactly the same composition with natural sapphire, but comes at a lower price. Sapphire is especially good at being scratch and crack resistant, being the second hardest element after diamond on the Mohs scale of mineral hardness, sapphire scoring 9 and diamond a 10. This can keep your watch looking brand new, even after constant use. Due to these properties sapphire is commonly used in luxury watches, but due to high manufacturing costs, as well as engineering costs (requiring diamond tipped cutters to cut), the use of it can be pricey.
The use of sapphire is not without its downsides however – one major disadvantage is that sapphire crystals are brittle and therefore prone to chips, and may even shatter. If this happens sapphire crystals can get in the movement and cause damage.
Mineral glass is a fancy word for ordinary glass which has been heated or chemically treated to increase scratch and shatter resistance. Mineral crystals are quite durable but less durable than acrylic crystals. They normally place around 5 on the Mohs scale of mineral hardness. They will get some scratches eventually and not as easy to be polished as acrylic crystals. This type of crystal is generally used on low-mid price range watches. A special type of treated mineral crystal exists also, called K1, which has a higher scratch resistance than mineral crystal.
Acrylic crystal, or plexiglass is similar to plastic – it is light, durable and the most affordable type of crystal. It is hard and cheaper to make however the only downside is it is prone to scratches. This material is suitable for childrens’ watches and alike, and is not used in luxury watches. Their advantage however is that they can be polished to remove small scratches.
Although sapphire crystals are the hardest and most scratch resistant of the crystals, care must still be taken so as to avoid unnecessary damage to your watch. As there is no perfect protection for a watch, as hard impacts may still damage sapphire, it must be wrapped when not in use with a cloth or something alike. Also avoid direct contact with other jewellery, for example gem and metallic edges. Due to its hardness, sapphire is often believed to be easy to chip or shatter, and therefore care should be taken when wearing it so as to not catch it on things, and reduce the risk of physical abuse, for example when playing sport.
Unfortunately when a crystal is cracked or heavily scratched immediate replacement is required since dust and water can penetrate and get into the movement. This can permanently damage the watch, or at least affect its performance. Ultimately, no matter what your watches crystal is made of do your best to maintain and preserve your watch – take care of it and it will take care of you!