Impregnation with plastic, however, makes these materials attractive and durable. When chalky turquoise is impregnated, it is called stabilization. Many designers prefer to use stabilized turquoise because this enhancement process actually strengthens stones. Dyeing Colorless to near-colorless gems benefit from dyeing with a coloring agent. Saltwater cultured pearls are immersed in a very light pink dye to give them an appealing rosy tint which makes it much easier to match colors for uniform necklaces.
All black onyx starts out a much lighter gray.
With dyeing, it becomes the familiar dramatic black that jewelers refer to as black onyx. And, it is important to remember that dyeing does much more than add color where there was little or none it also improves color uniformity. Many pieces of lapis lazuli, for example, have a patchy blue color that dyeing evens out. Other popular gems that are sometimes dyed are very low grades of coral, emerald, jadeite, opal and ruby. Bleaching Organic substances like ivory and pearl come from nature with various discolorations.