It entails the melting from the Uncooked compound using oxyhydrogen flame and also the crystallisation on the melted droplets to type a cylinder. Graded 9 on the Mohs-hardness scale (graded one-10), the ensuing sapphire crystals are just about scratch-evidence and very challenging, ensuring an unhindered vision all of the time. https://www.watchesworld.com/top-10-dive-watches/