The dangers of the WWW. I went looking for this month's birthstone and became lost for hours. Those delightful earrings have as their centre piece, "Chocolate" pearls, a product of a bleaching process developed by Ballerina Pearls.
The Gemmological Institute of America conducted a series of spectroscopic tests, Infra-red, Near Infra-red Reflectance, Raman and Photo luminescence on chocolate cultured pearls, silver dyed Tahitian cultured pearls and natural colour Tahitian cultured pearls.
They also cut into two pearls to a depth of 1mm (pearl on the left) and a deeper cut toward the nucleus (pearl on the right). The induced colouration appeared homogenous throughout both pearls. The GIA deduced that the treatment alters the organic components of the pearl nacre unlike an introduced dye.
A dye or stain will only penetrate the top layers of nacre, lessening in intensity toward the nucleus. This dyeing process (using silver nitrate) will also work on white or grey South Sea pearls. Dyed "chocolate" pearls are considered a "treated" pearl.