It requires the melting on the raw material making use of oxyhydrogen flame and also the crystallisation with the melted droplets to form a cylinder. Graded 9 within the Mohs-hardness scale (graded one-ten), the resulting sapphire crystals are virtually scratch-proof and really challenging, guaranteeing an unhindered eyesight all the time. https://www.watchesworld.com/top-10-dive-watches/