It includes the melting of your raw compound applying oxyhydrogen flame and also the crystallisation with the melted droplets to sort a cylinder. Graded 9 over the Mohs-hardness scale (graded one-ten), the ensuing sapphire crystals are just about scratch-proof and very difficult, making sure an unhindered vision all the time. https://www.watchesworld.com/top-10-dive-watches/