It requires the melting with the raw compound applying oxyhydrogen flame plus the crystallisation from the melted droplets to form a cylinder. Graded nine about the Mohs-hardness scale (graded one-ten), the resulting sapphire crystals are nearly scratch-proof and really hard, ensuring an unhindered vision always. four. Thickness When considered from https://www.watchesworld.com/the-most-coveted-watches-in-the-uk/