It involves the melting with the Uncooked substance working with oxyhydrogen flame along with the crystallisation from the melted droplets to type a cylinder. Graded nine over the Mohs-hardness scale (graded 1-10), the resulting sapphire crystals are nearly scratch-evidence and very hard, making certain an unhindered vision at all times. https://www.watchesworld.com/top-10-dive-watches/