It requires the melting of your raw material utilizing oxyhydrogen flame as well as crystallisation of the melted droplets to kind a cylinder. Graded 9 within the Mohs-hardness scale (graded one-10), the resulting sapphire crystals are nearly scratch-proof and very tricky, making sure an unhindered eyesight all of the time. https://www.watchesworld.com/top-10-dive-watches/