It requires the melting with the raw compound using oxyhydrogen flame as well as the crystallisation from the melted droplets to sort a cylinder. Graded 9 around the Mohs-hardness scale (graded 1-10), the resulting sapphire crystals are almost scratch-proof and really really hard, making certain an unhindered eyesight at all https://www.watchesworld.com/the-most-coveted-watches-in-the-uk/