It consists of the melting from the raw substance using oxyhydrogen flame and also the crystallisation on the melted droplets to variety a cylinder. Graded nine on the Mohs-hardness scale (graded 1-ten), the resulting sapphire crystals are nearly scratch-evidence and very challenging, ensuring an unhindered eyesight always. Useful cookies Useful https://www.watchesworld.com/top-10-dive-watches/