It entails the melting on the Uncooked compound applying oxyhydrogen flame and the crystallisation from the melted droplets to type a cylinder. Graded 9 within the Mohs-hardness scale (graded one-10), the ensuing sapphire crystals are pretty much scratch-evidence and really really hard, making sure an unhindered eyesight at all times. https://www.watchesworld.com/top-10-dive-watches/