It requires the melting of your Uncooked compound applying oxyhydrogen flame and also the crystallisation on the melted droplets to variety a cylinder. Graded 9 over the Mohs-hardness scale (graded one-10), the ensuing sapphire crystals are pretty much scratch-evidence and very tough, ensuring an unhindered eyesight all of the time. https://www.watchesworld.com/top-10-dive-watches/