It involves the melting in the raw material making use of oxyhydrogen flame and the crystallisation from the melted droplets to sort a cylinder. Graded 9 within the Mohs-hardness scale (graded 1-10), the ensuing sapphire crystals are practically scratch-evidence and really difficult, guaranteeing an unhindered vision continually. Practical cookies Useful https://www.watchesworld.com/top-10-dive-watches/