How Are Pearls Treated, and How Can You Tell?

Treatment is the rule rather than the exception for cultured pearls. CIBJO’s guide says almost all cultured pearls on the market have undergone some form of treatment, so a finished pearl’s color is a blend of its natural color at harvest and the changes made to it.¹

Why pearls are treated#

Few pearls come out of the oyster ready to sell. Because of variations in color and surface defects, more than 90% of cultured pearls can’t be used directly in jewelry, and processing to improve their color and surface is routine for Akoya and freshwater pearls.⁷

Some steps don’t count as treatments. CIBJO calls drilling, cutting, polishing and cleaning normal procedures. Treatments are processes beyond those that alter a pearl’s color, composition, appearance or durability.⁵

The main treatments#

• Bleaching removes or changes color with chemicals or light.⁵ It is common for Akoya and for Chinese freshwater pearls, and in Akoya processing it may be followed by choshoku, a light color adjustment to improve the tone.¹
• Dyeing applies a dye or stain to change the color.⁵ Dyeing and irradiation are the most common color treatments.⁶
• Irradiation exposes pearls to radiation to change their appearance.⁵ It has been used on freshwater cultured pearls since the 1960s, darkening their manganese-rich nacre.³ In Akoya pearls, it darkens the freshwater-shell bead inside, which changes the pearl’s color, luster and overtone.³
• Heating can alter a pearl’s appearance,⁵ and some yellow South Sea pearls are reportedly colored by a method involving heat.⁸
• Coating, waxing and oiling add a layer to the surface, to protect it, change its color or improve its luster, or soak it in oil to make cracks less visible.⁵
• Maeshori is a multi-part chemical treatment, with heat or light, that temporarily enhances luster.⁵
• Optical brightening, also called fluorescence whitening, applies chemicals that absorb ultraviolet light and give off blue fluorescence.⁵ It is routinely applied to untreated, naturally colored freshwater cultured pearls.⁶

Treatments by pearl type#

The Learn About Pearls dataset records the main identification and treatment notes for each cultured pearl type:

• Akoya: X-ray radiography shows the shell bead and lets labs measure the nacre over it. White Akoya are routinely processed after harvest. Bleaching is common, and the pink overtone is very often the result of processing. Bead-cultured freshwater pearls can look much the same. Freshwater pearls contain more manganese and barium and less strontium, a difference labs can measure.^{1 6 9 10 11 12}
• Freshwater: Freshwater pearls contain more manganese and barium and less strontium than saltwater pearls. Labs measure this directly, and through X-ray luminescence, which brightens with manganese. Some bead-cultured freshwater pearls look like Akoya and are sold as "freshwater Akoya", a name GIA calls incorrect. Bleaching, dyeing and optical brightening are common treatments.^{5 6 11 12 13}
• South Sea: X-ray radiography and microtomography show the bead and help separate bead-cultured, non-bead cultured and natural pearls. Golden color can be natural, or produced by heat or dye; labs tell them apart with UV-visible spectroscopy, fluorescence and photoluminescence.^{8 9 14 15 16}
• Tahitian: A reflectance feature near 700 nm is a key sign of the black-lipped oyster; pearls from Pinctada mazatlanica share it. Some are treated, for example bleached to "chocolate" brown or modified to "pistachio" green. French Polynesian law requires treated pearls to be labeled as treated.^{4 17 18 19 20}

How labs detect treatments#

Labs combine a microscope with instruments. GIA identifies treatments with standard gem testing plus real-time X-radiography, UV-Vis reflectance spectroscopy and X-ray fluorescence.²¹

• Golden color. Natural golden pearls from Pinctada maxima show an ultraviolet absorption feature like that of the oyster’s yellow shell, which is weak or absent in pearls reportedly colored by heat.⁸ Atypical absorption at 405 and 558 nm, with unusual brownish orange fluorescence, has identified treatment even when that feature was present.¹⁵ Dyes can leave little surface evidence, so labs rely on UV-visible reflectance and Raman photoluminescence spectroscopy.¹⁶
• Irradiated Akoya. Signs include color concentrated at the drill hole, an unnatural patchy surface, and a darkened bead visible inside.³
• “Chocolate” pearls. These were identified by their unusual coloration, their fluorescence, their reflectance and Raman spectra and their trace elements.⁴
• Freshwater pearls. GIA confirmed color treatment and optical brightening in freshwater “Edison” pearls by combining microscopy, UV fluorescence, fluorescence spectroscopy, Raman spectroscopy and trace-element analysis.⁶

How long treatments last#

Bleaching and irradiation can be stable during normal wear.² Some color-treated pearls, though, can fade or revert to their original color in sunlight, artificial light or strong display lights.⁵ Maeshori enhances luster only temporarily, and CIBJO requires sellers to declare when a process isn’t permanent and the pearls need special care.⁵

What sellers must tell you#

CIBJO’s standards require treatments such as bleaching, coating, dyeing, filling, heating, irradiation, maeshori, oiling, tinting, optical brightening and waxing to be declared when cultured pearls are sold. The treatment must be named next to the words “cultured pearl” or the color description, and explained to the buyer before the sale closes.⁵ CIBJO’s guide adds that a pearl’s color and luster should be clearly identified as treated or untreated.¹

French Polynesia’s pearl law defines the Tahitian cultured pearl as naturally colored and untreated, and requires treated pearls to be labeled “traitées” (treated) or with the name of the treatment.²⁰

A laboratory report records any detectable treatment.^{11 22}