It involves the melting of your raw material using oxyhydrogen flame as well as the crystallisation in the melted droplets to sort a cylinder. Graded 9 around the Mohs-hardness scale (graded 1-ten), the ensuing sapphire crystals are nearly scratch-proof and really difficult, making certain an unhindered vision at all times. https://www.watchesworld.com/top-10-dive-watches/