It involves the melting with the raw substance applying oxyhydrogen flame as well as crystallisation of the melted droplets to sort a cylinder. Graded 9 about the Mohs-hardness scale (graded one-10), the ensuing sapphire crystals are almost scratch-proof and very challenging, ensuring an unhindered eyesight at all times. Purposeful cookies https://www.watchesworld.com/top-10-dive-watches/