It entails the melting in the Uncooked substance utilizing oxyhydrogen flame as well as crystallisation in the melted droplets to form a cylinder. Graded nine over the Mohs-hardness scale (graded 1-10), the ensuing sapphire crystals are just about scratch-evidence and very tough, making sure an unhindered vision at all times. https://www.watchesworld.com/top-10-dive-watches/