How to distinguish whether the sapphire mirror is coated or not

The simplest way to distinguish is to tilt the mirror surface, and the effect of thin film interference will cause it to present colored light (like a pair of glasses).
When buying a watch, when you hear that it uses a sapphire mirror, you will definitely feel that the watch is very tall and stylish. But in reality, the sapphires used on watches are not expensive natural sapphires, but genuine artificial sapphires.