It consists of the melting of your raw substance using oxyhydrogen flame and also the crystallisation with the melted droplets to form a cylinder. Graded 9 over the Mohs-hardness scale (graded one-ten), the ensuing sapphire crystals are almost scratch-proof and really tough, ensuring an unhindered vision all of the time. https://www.watchesworld.com/top-10-dive-watches/