It involves the melting of the raw substance applying oxyhydrogen flame plus the crystallisation in the melted droplets to variety a cylinder. Graded nine around the Mohs-hardness scale (graded one-ten), the ensuing sapphire crystals are practically scratch-evidence and very tough, making certain an unhindered vision always. Practical cookies Useful cookies https://www.watchesworld.com/the-most-coveted-watches-in-the-uk/