It includes the melting of the raw compound employing oxyhydrogen flame and also the crystallisation from the melted droplets to sort a cylinder. Graded 9 around the Mohs-hardness scale (graded one-ten), the resulting sapphire crystals are nearly scratch-evidence and very tough, making certain an unhindered vision all of the time. https://www.watchesworld.com/top-10-dive-watches/