There are some treatments to take note of on cultured pearls that will change the aesthetic qualities of the pearl.
After harvesting cleaning and polishing a low-quality cultured pearl if the pearl still does not have a good luster or color, the farmer has very few options. If the pearls is a good candidate for treatment, this is the most common and economically sensible thing for the farmer to do. There are three main treatments are used on low-quality pearls.
Dyeing- The use of silver nitrate to darken the nacre of the pearl. Irradiation- The use of gamma rays to darken the nucleus of the pearl in akoya pearls and the nacre layers in freshwater pearls. Luster treatments- A coating is placed on the surface of the pearl to enhance the luster.
Silver nitrate has been used for decades to darken the appearance of the peal. The chemical penetrates the layer of nacre and has a chemical reaction with light or hydrogen sulfides gas to organic or inorganic dyes to produce another color variation. This treatment is very popular in treating fresh water pearls. Sometimes the farmer will want to create other colors then black the farmer in this case can use organic or inorganic dyes to make the color variations. Akoya pearls are also routinely “pinked” this is done when they would like to make a more rose overtone.
Irradiation has a different effect on freshwater to saltwater and cultured pearls. Gamma rays do not affect the nacre layers of a saltwater cultured pearl, but will darken the nucleus of the pearl. Saltwater pearls that are irradiated will be gray to blue. Freshwater irradiated pearls can become very dark, some of these freshwater treated pearls may also have an intense metallic sheen over their surface.
Coating a pearls to enhance its luster is not widely practiced and is frowned upon. The coating is like putting clear nail polish. The coating may eventually chip or peel, leaving a low-luster pearl this is a treatment to watch for.
Luster treatments are very hard to find. The most basic way to find the luster treatment is to compare an untreated strand with the strand that you think has been treated. You can put the strand under 50x magnification. The untreated pearl will have a scaly nacre surface and the coated pearl will have a smooth, glass like surface.