It consists of the melting of the raw material using oxyhydrogen flame as well as the crystallisation on the melted droplets to kind a cylinder. Graded 9 to the Mohs-hardness scale (graded 1-10), the ensuing sapphire crystals are just about scratch-evidence and really tricky, making sure an unhindered vision continually. https://www.watchesworld.com/top-10-dive-watches/