It includes the melting of the raw substance working with oxyhydrogen flame and the crystallisation in the melted droplets to variety a cylinder. Graded 9 around the Mohs-hardness scale (graded 1-ten), the resulting sapphire crystals are virtually scratch-evidence and very really hard, ensuring an unhindered vision all of the time. https://www.watchesworld.com/top-10-dive-watches/