We all know that Sapphire Crystal is harder than Glass, however it does have a higher index of refraction which makes it more light reflective. This of course hinders reading the time. For that reason watch manufactures apply anti-reflaction coatings that get rid of the problem. More than one transparent thin layers create a destructive interference between waves hence almost bringing reflective light to zero. While most watch manufacturers apply reflective coating only to the inside part of the crystal, it can applied to the outside as well. The advantage of applying outside is that reflection approximates more to under 1% reflection while only one side is more around 5%. There are few brands such as Breitling watches and Dubey & Schaldenbrand that prefer coating on both sides. The disadvantage of applying coating on both sides is that with time the outside part of the sapphire crystal may appear to be scratched. In reality it is the coating that is scratched giving a bad appearance. The only way to fix that problem is to polish the the crystal, removing the antireflection altogether.

Breitling Navitimer with Anti-Reflective Coating

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