It involves the melting in the raw compound working with oxyhydrogen flame and also the crystallisation on the melted droplets to variety a cylinder. Graded 9 around the Mohs-hardness scale (graded one-ten), the resulting sapphire crystals are pretty much scratch-proof and very tricky, ensuring an unhindered eyesight at all times. https://www.watchesworld.com/top-10-dive-watches/