It consists of the melting in the raw material using oxyhydrogen flame and also the crystallisation in the melted droplets to type a cylinder. Graded 9 around the Mohs-hardness scale (graded 1-10), the ensuing sapphire crystals are virtually scratch-proof and really really hard, guaranteeing an unhindered eyesight all the time. https://www.watchesworld.com/top-10-dive-watches/