[callalex]

I wonder if the process would be cheaper than the current high end (smart)watch and lens practice of sapphire coating?

[namibj]

No, it's substantially more expensive. At least for anything too large to just cut out of HPHT chunks, just due to CVD at optical grade being pretty slow.

[Animats]

Diamond coated glass is available and is sometimes used for checkout lane scanners.[1] It's not common.

[1] https://www.diamonex.com/wear-resistant-glass/