It involves the melting in the raw substance working with oxyhydrogen flame plus the crystallisation in the melted droplets to type a cylinder. Graded nine within the Mohs-hardness scale (graded 1-10), the resulting sapphire crystals are just about scratch-evidence and very tough, making certain an unhindered eyesight at all times. https://www.watchesworld.com/top-10-dive-watches/