It entails the melting of the raw compound working with oxyhydrogen flame and the crystallisation in the melted droplets to form a cylinder. Graded 9 within the Mohs-hardness scale (graded one-10), the ensuing sapphire crystals are almost scratch-proof and very really hard, ensuring an unhindered eyesight all of the time. https://www.watchesworld.com/top-10-dive-watches/