ELISABETH NEWTON PEARLS
Pearl coloration and treatments are a tricky topic: advancement of treatment processes result in a larger range of pearl colors available on the market. Natural pearls come in natural colors: white, cream, black, grey, sometimes champagne. So what’s with all the others?
D Y E S : Because pearls are porous, they make for a great surface for dyes. Silver nitrate is used to darken the outer nacre (coating) of the pearl. Dyes often fade over time, as they are a superficial treatment to the outer layer.
I R R A D I A T I O N : Irradiation is the bombardment of a pearl with gamma-rays. Irradiation darkens the nucleus and results in a darker shade of the natural pearl. This treatment is most often used to mimic black or South Sea pearls. Irradiation also heightens the luster and iridescence of the pearl. (Not to worry though, pearls cannot retain radiation)
Next question: how do you tell if a pearl has been irradiated or dyed? This is a little tougher, but my recommendation is to first check the drill hole of the pearl. Dyes only permeate the surface of a pearl, thereby often leaving a visible rim along the drill hole. You can also sometimes see the natural color of the pearl underneath, or the darkened nucleus inside, which is indicative of irradiation. Another trick is to check the matching of a strand. Natural pearls vary in color: if a strand is consistent it is more than likely treated.