It entails the melting of the raw material 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 practically scratch-evidence and very hard, ensuring an unhindered eyesight all the time. Afterwards illustrations https://www.watchesworld.com/top-10-dive-watches/