Sapphire and Ruby ball lenses are both made by melting aluminum oxide at a temperature higher than 2000 º C. Ruby owes its red colour to traces of chromium oxide (chromium content for ruby balls is typically less than 0.5%). While their physical and chemical properties are basically the same, their optical properties are somewhat different. Sapphire has superior optical transmission qualities.
Due to the refractive index of sapphire (1.760), it is ideal to be used as a sapphire ball lens for optical telecom products. In addition to the optical properties of sapphire, it is also wear resistant and can withstand severe chemical corrosion.