Allochromatic gems are gems that are colored by impurities. When they have been entirely pure, they might be colorless. The colour of all allochromatic gems is produced by defects. Therefore, all coloration in corundum is because of defects. Certification: The presence of a credible gemological certification from a dependable and https://www.tumblr.com/thegemjournal/759696203354128384/understanding-the-unique-characteristics-of-yellow?source=share