---
title: "How Are Pearls Treated, and How Can You Tell?"
description: "Pearl treatments from bleaching and dyeing to irradiation, heating and coating: how labs detect them, how long they last, and what sellers must disclose."
canonical_url: "https://learnaboutpearls.com/identification/dyed-and-treated-pearls/"
last_updated: "2026-11-04"
last_reviewed: "2026-10-26"
reviewed_by: "Simon"
publisher: "Unique Pearl"
publisher_disclosure: "Learn About Pearls is published by Unique Pearl, a pearl jeweler."
---
# How Are Pearls Treated, and How Can You Tell?

**Short answer:** Most cultured pearls are treated in some way after the harvest. Common treatments include bleaching, dyeing, irradiation, heating, coating, luster treatments such as maeshori, and optical brighteners. Some, such as bleaching and irradiation, can be stable in normal wear, while others can fade. Under CIBJO's standards, treatments must be disclosed when pearls are sold, and labs look for them with magnification, UV light, spectroscopy and chemical analysis.

**Key facts:**

- CIBJO's guide says almost all cultured pearls on the market have undergone some form of treatment. [1]
- Color is the quality factor most affected by treatments. [1]
- Bleaching and irradiation can be stable during normal wear. [2]
- Irradiation has darkened freshwater cultured pearls since the 1960s. In Akoya pearls it darkens the freshwater-shell bead inside, changing the pearl's color, luster and overtone. [3]
- "Chocolate" pearls were most likely made by bleaching black cultured pearls; GIA found no added coloring agent. [4]
- Under CIBJO's standards, a treatment must be named next to the words "cultured pearl" and explained to the buyer before the sale closes. [5]
- Optical brighteners are routinely applied to untreated, naturally colored freshwater cultured pearls after harvest. [6]

Treatment is the rule rather than the exception for [cultured pearls](https://learnaboutpearls.com/glossary/#cultured-pearl). 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](https://learnaboutpearls.com/glossary/#akoya) and [freshwater pearls](https://learnaboutpearls.com/glossary/#freshwater-cultured-pearl). [7]

Some steps don’t count as treatments. CIBJO calls [drilling](https://learnaboutpearls.com/glossary/#drilled), cutting, [polishing](https://learnaboutpearls.com/glossary/#polishing) and cleaning [normal procedures](https://learnaboutpearls.com/glossary/#normal-procedures). Treatments are processes beyond those that alter a pearl’s color, composition, appearance or durability. [5]

## The main treatments

- **[Bleaching](https://learnaboutpearls.com/glossary/#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](https://learnaboutpearls.com/glossary/#dyeing)** applies a dye or stain to change the color. [5] Dyeing and [irradiation](https://learnaboutpearls.com/glossary/#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](https://learnaboutpearls.com/glossary/#nacre). [3] In Akoya pearls, it darkens the [freshwater-shell bead](https://learnaboutpearls.com/glossary/#bead) inside, which changes the pearl’s color, [luster](https://learnaboutpearls.com/glossary/#luster) and [overtone](https://learnaboutpearls.com/glossary/#overtone). [3]
- **[Heating](https://learnaboutpearls.com/glossary/#heating)** can alter a pearl’s appearance, [5] and some yellow [South Sea pearls](https://learnaboutpearls.com/glossary/#south-sea-cultured-pearl) are reportedly colored by a method involving heat. [8]
- **[Coating](https://learnaboutpearls.com/glossary/#coating), [waxing](https://learnaboutpearls.com/glossary/#waxing) and [oiling](https://learnaboutpearls.com/glossary/#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](https://learnaboutpearls.com/glossary/#maeshori)** is a multi-part chemical treatment, with heat or light, that temporarily enhances luster. [5]
- **[Optical brightening](https://learnaboutpearls.com/glossary/#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](https://learnaboutpearls.com/glossary/#x-radiography), UV-Vis reflectance spectroscopy and X-ray fluorescence. [21]

- **Golden color.** Natural golden pearls from _[Pinctada maxima](https://learnaboutpearls.com/glossary/#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](https://learnaboutpearls.com/glossary/#treated-pearl), 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](https://learnaboutpearls.com/glossary/#special-care). [5]

## What sellers must tell you

CIBJO’s standards require treatments such as bleaching, coating, dyeing, [filling](https://learnaboutpearls.com/glossary/#filling), heating, irradiation, maeshori, oiling, [tinting](https://learnaboutpearls.com/glossary/#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](https://learnaboutpearls.com/glossary/#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](https://learnaboutpearls.com/glossary/#laboratory-report) records any detectable treatment. [11, 22]

## Questions people ask

### What are chocolate pearls?

Brown cultured pearls whose color comes from treatment. GIA's study of one company's "chocolate" pearls found that black cultured pearls had most likely been bleached to turn them brown, with no added coloring agent, and such pearls had reached the market from several sources. [4]

### Do treated pearls lose their color?

Some can. CIBJO notes that some color-treated pearls may fade or revert to their original color under sunlight, artificial light or strong display lights, and requires sellers to declare any treatment that isn't permanent. GIA says bleaching and irradiation can be stable in normal wear. [2, 5]

### Can you tell if a pearl is dyed or irradiated by looking?

Sometimes. Irradiated Akoya can show color concentrated at the drill hole or an unnatural patchy surface. But some dyed golden pearls show little surface evidence, and labs rely on UV-visible reflectance and Raman photoluminescence spectroscopy to identify them. [3, 16]

### Is bleaching a treatment?

Yes. CIBJO lists bleaching among the treatments that must be declared when cultured pearls are sold. Drilling, cutting, polishing and cleaning, by contrast, are normal procedures, not treatments. [5]

## References

1. CIBJO Pearl Commission (2025). CIBJO Guides Describing and Classifying Natural and Cultured Pearls, the Producing Molluscs & Responsible Pearling. [Source](https://cibjo.org/wp-content/uploads/2025/12/Final-Guide-October-2025-v2-COMPRESSED.pdf) · [Archived copy](https://web.archive.org/web/20260212155210/https://cibjo.org/wp-content/uploads/2025/12/Final-Guide-October-2025-v2-COMPRESSED.pdf)
2. Gemological Institute of America (GIA), Gem Encyclopedia. Pearl Buyer's Guide. [Source](https://www.gia.edu/pearl/buyers-guide) · [Archived copy](https://web.archive.org/web/20260613185853/https://www.gia.edu/pearl/buyers-guide)
3. Emiko Yazawa and Chunhui Zhou (2024). Irradiated and Dyed Akoya Pearls. [Source](https://www.gia.edu/gems-gemology/spring-2024-lab-notes-irradiated-and-dyed-akoya-pearls) · [Archived copy](https://web.archive.org/web/20240720120748/https://www.gia.edu/gems-gemology/spring-2024-lab-notes-irradiated-and-dyed-akoya-pearls)
4. Wuyi Wang, Kenneth Scarratt, Akira Hyatt, Andy Hsi-Tien Shen and Matthew Hall (2006). Identification of "Chocolate Pearls" Treated by Ballerina Pearl Co.. [Source](https://www.gia.edu/gems-gemology/winter-2006-identification-chocolate-pearls-ballerina-co-wang) · DOI [10.5741/GEMS.42.4.222](https://doi.org/10.5741/GEMS.42.4.222) · [Archived copy](https://web.archive.org/web/20260411054259/https://www.gia.edu/gems-gemology/winter-2006-identification-chocolate-pearls-ballerina-co-wang)
5. CIBJO, The World Jewellery Confederation, Pearl Commission (2026). The CIBJO Pearl Book (Pearl Blue Book) 2026. [Source](https://cibjo.org/wp-content/uploads/2026/10/Pearl-Blue-Book-2026-.pdf) · [Archived copy](https://web.archive.org/web/20261025235254/https://cibjo.org/wp-content/uploads/2026/10/Pearl-Blue-Book-2026-.pdf)
6. Chunhui Zhou and others (2021). Detection of Color Treatment and Optical Brightening in Chinese Freshwater "Edison" Pearls. [Source](https://www.gia.edu/gems-gemology/summer-2021-detection-of-color-treatment-and-optical-brightening-in-chinese-freshwater-edison-pearls) · DOI [10.5741/GEMS.57.2.124](https://doi.org/10.5741/GEMS.57.2.124) · [Archived copy](https://web.archive.org/web/20260413154357/https://www.gia.edu/gems-gemology/summer-2021-detection-of-color-treatment-and-optical-brightening-in-chinese-freshwater-edison-pearls)
7. Changbo Zhu, Paul C. Southgate and Ting Li (2019). Production of Pearls. [Source](https://link.springer.com/chapter/10.1007/978-3-319-96776-9_5) · DOI [10.1007/978-3-319-96776-9_5](https://doi.org/10.1007/978-3-319-96776-9_5) · [Archived copy](https://web.archive.org/web/20240129152149/https://link.springer.com/chapter/10.1007/978-3-319-96776-9_5)
8. Shane Elen (2001). Spectral Reflectance and Fluorescence Characteristics of Natural-Color and Heat-Treated "Golden" South Sea Cultured Pearls. [Source](https://www.gia.edu/gems-gemology/summer-2001-heat-treated-golden-south-sea-cultured-pearls-elen) · DOI [10.5741/GEMS.37.2.114](https://doi.org/10.5741/GEMS.37.2.114) · [Archived copy](https://web.archive.org/web/20260308065638/https://www.gia.edu/gems-gemology/summer-2001-heat-treated-golden-south-sea-cultured-pearls-elen)
9. Chunhui Zhou and W. Henry Towbin (2024). Applications of X-Ray Radiography and X-Ray Computed Microtomography in Gemology. [Source](https://www.gia.edu/gems-gemology/winter-2024-x-ray-imaging) · DOI [10.5741/GEMS.60.4.582](https://doi.org/10.5741/GEMS.60.4.582) · [Archived copy](https://web.archive.org/web/20260313113455/https://www.gia.edu/gems-gemology/winter-2024-x-ray-imaging)
10. Artitaya Homkrajae (2024). Remarkably Large Akoya Bead Cultured Pearls. [Source](https://www.gia.edu/gems-gemology/summer-2024-gemnews-large-akoya-bead-cultured-pearls) · [Archived copy](https://web.archive.org/web/20261025235607/https://www.gia.edu/gems-gemology/summer-2024-gemnews-large-akoya-bead-cultured-pearls)
11. Phoebe Shang (2026). Freshwater Akoyas – A Trending Misnomer for Certain Freshwater Pearls. [Source](https://www.gia.edu/freshwater-akoyas-a-trending-misnomer-for-certain-pearls) · [Archived copy](https://web.archive.org/web/20260617073835/https://www.gia.edu/freshwater-akoyas-a-trending-misnomer-for-certain-pearls)
12. Stefanos Karampelas and others (2019). Chemical Characteristics of Freshwater and Saltwater Natural and Cultured Pearls from Different Bivalves. [Source](https://www.mdpi.com/2075-163X/9/6/357) · DOI [10.3390/min9060357](https://doi.org/10.3390/min9060357) · [Archived copy](https://web.archive.org/web/20261012102331/https://www.mdpi.com/2075-163X/9/6/357)
13. H. A. Hänni (2006). A short review of the use of "keshi" as a term to describe pearls. [Source](https://www.ssef.ch/wp-content/uploads/2018/03/2006_Haenni_A_short_review_of_the_use_of_Keshi_as_a_term_to_describe_pearls.pdf) · DOI [10.15506/JoG.2006.30.1.51](https://doi.org/10.15506/JoG.2006.30.1.51) · [Archived copy](https://web.archive.org/web/20260416052623/https://www.ssef.ch/wp-content/uploads/2018/03/2006_Haenni_A_short_review_of_the_use_of_Keshi_as_a_term_to_describe_pearls.pdf)
14. Artitaya Homkrajae, Nanthaporn Nilpetploy, Areeya Manustrong, Nicholas Sturman, Kwanreun Lawanwong and Promlikit Kessrapong (2021). Internal Structures of Known Pinctada maxima Pearls: Cultured Pearls from Operated Marine Mollusks. [Source](https://www.gia.edu/gems-gemology/fall-2021-internal-structures-pinctada-maxima-pearls) · DOI [10.5741/GEMS.57.3.186](https://doi.org/10.5741/GEMS.57.3.186) · [Archived copy](https://web.archive.org/web/20260420034834/https://www.gia.edu/gems-gemology/fall-2021-internal-structures-pinctada-maxima-pearls)
15. Shane Elen (2002). Update on the Identification of Treated "Golden" South Sea Cultured Pearls. [Source](https://www.gia.edu/gems-gemology/summer-2002-identification-treated-golden-south-sea-pearls-elen) · DOI [10.5741/GEMS.38.2.156](https://doi.org/10.5741/GEMS.38.2.156) · [Archived copy](https://web.archive.org/web/20260116222127/https://www.gia.edu/gems-gemology/summer-2002-identification-treated-golden-south-sea-pearls-elen)
16. Chunhui Zhou, Artitaya Homkrajae, Joyce Wing Yan Ho, Akira Hyatt and Nicholas Sturman (2012). Update on the Identification of Dye Treatment in Yellow or "Golden" Cultured Pearls. [Source](https://www.gia.edu/gems-gemology/winter-2012-cultured-pearls-zhou) · DOI [10.5741/GEMS.48.4.284](https://doi.org/10.5741/GEMS.48.4.284) · [Archived copy](https://web.archive.org/web/20260309094817/https://www.gia.edu/gems-gemology/winter-2012-cultured-pearls-zhou)
17. Artitaya Homkrajae (2016). Spectral Characteristics of Pinctada mazatlanica and Pinctada margaritifera Pearl Oyster Species. [Source](https://www.gia.edu/gems-gemology/summer-2016-gemnews-spectral-characteristics-pinctada-mazatlanica-margaritifera-pearl-oyster-species) · [Archived copy](https://web.archive.org/web/20260317034153/https://www.gia.edu/gems-gemology/summer-2016-gemnews-spectral-characteristics-pinctada-mazatlanica-margaritifera-pearl-oyster-species)
18. Stefanos Karampelas, Emmanuel Fritsch, Jean-Pierre Gauthier and Thomas Hainschwang (2011). UV-Vis-NIR Reflectance Spectroscopy of Natural-Color Saltwater Cultured Pearls from Pinctada margaritifera. [Source](https://www.gia.edu/doc/UV-VIS-NIR-Reflectance-Spectroscopy-of-Natural-Color-Saltwater-Cultured-Pearls-from-Pinctada-Margaritifera.pdf) · DOI [10.5741/GEMS.47.1.31](https://doi.org/10.5741/GEMS.47.1.31) · [Archived copy](https://web.archive.org/web/20260315140441/https://www.gia.edu/doc/UV-VIS-NIR-Reflectance-Spectroscopy-of-Natural-Color-Saltwater-Cultured-Pearls-from-Pinctada-Margaritifera.pdf)
19. Chunhui Zhou, Joyce Wing Yan Ho, Sally Chan, Jessie Yixin Zhou, Surjit Dillon Wong and Kyaw Soe Moe (2016). Identification of "Pistachio" Colored Pearls Treated by Ballerina Pearl Co.. [Source](https://www.gia.edu/gems-gemology/spring-2016-identification-pistachio-colored-pearls-treated-ballerina-pearl-company) · DOI [10.5741/GEMS.52.1.50](https://doi.org/10.5741/GEMS.52.1.50) · [Archived copy](https://web.archive.org/web/20260411201433/https://www.gia.edu/gems-gemology/spring-2016-identification-pistachio-colored-pearls-treated-ballerina-pearl-company)
20. Assemblée de la Polynésie française (Journal officiel de la Polynésie française) (2017). Loi du pays n° 2017-16 du 18 juillet 2017 réglementant les activités professionnelles liées à la production et la commercialisation des produits perliers et nacriers en Polynésie française. [Source](https://www.ressources-marines.gov.pf/wp-content/uploads/sites/24/2017/10/Loi-du-Pays-n%C2%B0-2017-16-du-18_07_2017-Activit%C3%A9s-professionnelles-perli.pdf) · [Archived copy](https://web.archive.org/web/20261026000126/https://www.ressources-marines.gov.pf/wp-content/uploads/sites/24/2017/10/Loi-du-Pays-n%C2%B0-2017-16-du-18_07_2017-Activit%C3%A9s-professionnelles-perli.pdf)
21. Gemological Institute of America (GIA), Analysis & Grading. How GIA Identifies and Classifies Pearls. [Source](https://www.gia.edu/gem-lab-how-gia-identifies-classifies-pearls) · [Archived copy](https://web.archive.org/web/20260606232640/https://www.gia.edu/gem-lab-how-gia-identifies-classifies-pearls)
22. Swiss Gemmological Institute SSEF. Pearls (SSEF reports). [Source](https://www.ssef.ch/reports/pearls/) · [Archived copy](https://web.archive.org/web/20260611191437/https://www.ssef.ch/reports/pearls/)

**Written by:** Learn About Pearls editors

**Fact-checked:** Learn About Pearls editors, October 26, 2026

**Reviewed by:** Simon, October 26, 2026

**First published:** November 4, 2026

**Publisher:** [Unique Pearl](https://learnaboutpearls.com/about/), a pearl jeweler

**Revision history**

1. November 4, 2026: First published. First published

**How to cite this page**

**APA:** Learn About Pearls editors. (2026). _How Are Pearls Treated, and How Can You Tell?_ Learn About Pearls. https://learnaboutpearls.com/identification/dyed-and-treated-pearls/

**MLA:** “How Are Pearls Treated, and How Can You Tell?” _Learn About Pearls_, Unique Pearl, November 4, 2026, learnaboutpearls.com/identification/dyed-and-treated-pearls/.

**Chicago:** Learn About Pearls editors. “How Are Pearls Treated, and How Can You Tell?” Learn About Pearls. Unique Pearl. Last modified November 4, 2026. https://learnaboutpearls.com/identification/dyed-and-treated-pearls/.

**BibTeX:** `@misc{lap-identification-dyed-and-treated-pearls, title = {How Are Pearls Treated, and How Can You Tell?}, author = {{Learn About Pearls editors}}, year = {2026}, howpublished = {\url{https://learnaboutpearls.com/identification/dyed-and-treated-pearls/}}, note = {Learn About Pearls, published by Unique Pearl}}`

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## Related pages

- [Is it a real pearl?](https://learnaboutpearls.com/identification/how-to-tell-if-pearls-are-real/): Simple checks that point to an imitation, what each one can and can't prove, and when to ask a lab.
- [Color and overtone](https://learnaboutpearls.com/quality/color-and-overtone/): The colors pearls come in, what overtone and orient mean, and how color affects value.
- [Tahitian pearls](https://learnaboutpearls.com/types/tahitian-pearls/): Dark, naturally colored cultured pearls from the black-lipped oyster of French Polynesia.