It will involve the melting on the Uncooked material using oxyhydrogen flame plus the crystallisation with the melted droplets to form a cylinder. Graded 9 on the Mohs-hardness scale (graded 1-10), the resulting sapphire crystals are pretty much scratch-proof and very tricky, ensuring an unhindered vision all of the time. https://www.watchesworld.com/top-10-dive-watches/