It requires the melting of the Uncooked compound working with oxyhydrogen flame as well as crystallisation in the melted droplets to form a cylinder. Graded 9 to the Mohs-hardness scale (graded one-10), the resulting sapphire crystals are practically scratch-proof and really hard, making certain an unhindered eyesight all the time. https://www.watchesworld.com/top-10-dive-watches/