English: The curvature observed in this synthetic color-change Sapphire is due to a process known as the Verneuil Process or, flame fusion. During this process, a fine crushed material is heated at extremely high temperatures. The crushed material is then melted which drips through a furnace onto a boule. This boule where the Corundum cools down and crystallizes, spins and thus causes the curved striations. Natural Corundum does not form this way and helps gemologists separate natural Corundum from synthetic Corundum.