It entails the melting of the raw material utilizing oxyhydrogen flame and the crystallisation of the melted droplets to form a cylinder. Graded nine on the Mohs-hardness scale (graded one-ten), the resulting sapphire crystals are practically scratch-evidence and very really hard, making certain an unhindered eyesight all of the time. https://www.watchesworld.com/top-10-dive-watches/