Strictly speaking, Sapphire crystals aren’t really Sapphire. The correct name for the material is corundum. Sapphire is used to describing the blue variety corundum, while ruby is used for the red variety.) A Sapphire crystal is a lab-grown crystal that has the same properties as a Sapphire; which rate a 9 on the Mohs scale of hardness. Diamonds which are the hardest substance on earth rate a 10. This crystal is then cut and polished and placed as the lens of the watch to protect the hands and dial. Sapphire crystals, which are often coated with an anti-reflective substance, are the hardest lens used on watches and are very difficult to scratch. The time consuming and labour-intensive process used to create and finish these crystals to exacting standards add to the rarity and value of a watch with a sapphire crystal.