Tell me more about crystal coatings / Mainspring Q&A - Answering your watch questions

Q: What is anti-reflective coating?

A: A low-reflection coating applied to a sapphire crystal with a high refractive index.

Anti-reflective coating (or more accurately, low-reflective coating) on ​​crystals is now becoming commonplace in luxury watches. This coating reduces light reflection, making the dial easier to read.

Glass coating is a technology invented in the late 19th century. However, it is said that it only became widespread in the watch industry after the 1990s, when sapphire crystal crystals became popular. Sapphire crystals have a higher refractive index than plastic crystals, which inevitably makes them less visible. For this reason, some manufacturers who pioneered the use of sapphire crystal crystals in the 80s began applying anti-reflective coatings to their sapphire crystals.

Initially, crystal coatings had the problem of low durability (i.e., they peeled easily), but as their durability has improved over the years, many manufacturers now use them. Even Rolex, which previously disliked anti-reflective coatings, has started to use them on some of its models, so the improvement in quality is clear.

Additionally, previous anti-reflective coatings had the problem of appearing green, purple, or blue, but now they are nearly transparent. As a result, manufacturers can now use a wide variety of colors on their watch dials. The main reason for the vibrant colors of watch dials is the evolution of coatings.

There are two types: coated on the inside only and coated on both sides

If you're only concerned with visibility, we recommend a double-sided anti-reflective coating, which has coatings on both the inside and outside of the crystal. However, if you rub the crystal hard, the outer coating may peel off. This doesn't happen much with modern watches, but it was common in watches from the 1990s and 2000s. In such cases, the crystal will need to be replaced, as it is virtually impossible to recoat it.

For this reason, some watches used for tough purposes have anti-reflective coating applied only to the inside of the crystal. For example, the German watch manufacturer Damascus offers two anti-reflective coatings on both sides or the inside depending on the purpose of use.

Incidentally, Japanese watch manufacturers are said to have the highest quality coatings in the watch industry. Citizen's "Clarity Coating" and Seiko's "Super Clear Coating" not only almost completely suppress reflections, but are also highly durable.