It includes the melting of the Uncooked material using oxyhydrogen flame and also the crystallisation in the melted droplets to form a cylinder. Graded 9 around the Mohs-hardness scale (graded one-10), the resulting sapphire crystals are pretty much scratch-proof and really tricky, making certain an unhindered vision all the time. https://www.watchesworld.com/top-10-dive-watches/