It entails the melting of the raw material using oxyhydrogen flame as well as crystallisation on the melted droplets to variety a cylinder. Graded 9 to the Mohs-hardness scale (graded one-ten), the resulting sapphire crystals are virtually scratch-evidence and very difficult, guaranteeing an unhindered eyesight at all times. Later illustrations https://www.watchesworld.com/top-10-dive-watches/