It consists of the melting in the raw material utilizing oxyhydrogen flame plus the crystallisation from the melted droplets to type a cylinder. Graded 9 within the Mohs-hardness scale (graded one-ten), the ensuing sapphire crystals are nearly scratch-proof and really really hard, making certain an unhindered vision all the time. https://www.watchesworld.com/top-10-dive-watches/