It entails the melting in the raw material employing oxyhydrogen flame as well as crystallisation from the melted droplets to variety a cylinder. Graded 9 over the Mohs-hardness scale (graded one-ten), the resulting sapphire crystals are pretty much scratch-evidence and very hard, ensuring an unhindered vision all of the time. https://www.watchesworld.com/top-10-dive-watches/