It involves the melting from the Uncooked compound using oxyhydrogen flame along with the crystallisation on the melted droplets to form a cylinder. Graded nine within the Mohs-hardness scale (graded one-ten), the ensuing sapphire crystals are just about scratch-evidence and really tough, making certain an unhindered vision at all times. https://www.watchesworld.com/top-10-dive-watches/