Color in Natural, Treated, and Synthetic Diamonds
For a colored diamond, three questions must be asked separately:
- Where did the material originate?
- How was the color produced?
- Was additional processing performed after growth?
A large share of errors in sales and in the interpretation of laboratory reports arises when these three questions are compressed into a single word—“natural,” “treated,” or “synthetic.”
The First Axis: Material Origin
The material may be:
- a natural diamond created by a geologic process in the Earth;
- a synthetic diamond (laboratory-grown) created by an industrial HPHT or CVD process.
This is a question of the genesis of the crystal, not its color.
A natural diamond may have treated color. A synthetic diamond may have color produced during growth without subsequent color treatment.
The Second Axis: Origin of Color
For a natural colored diamond, a laboratory may conclude, depending on the evidence and type of service, that the color is:
- of natural origin;
- the result of treatment;
- undetermined by the available methods.
Color grade describes the appearance of the color. Origin of color explains, to the extent possible, its cause and history.
They are not the same fields.
The Third Axis: Additional Treatment
After the crystal has formed, a natural or synthetic diamond may undergo a process that changes color or other properties.
The most important groups include:
- HPHT processing;
- irradiation;
- annealing;
- combinations of irradiation and annealing;
- surface coatings;
- processes that affect fractures or their visual appearance.
The detailed physics of these treatments belongs to Chapters 57–63. Here, only their position within the evidentiary model must be understood.
A Natural Diamond Does Not Automatically Have Natural Color
This is the most important sentence in the chapter.
A diamond may unquestionably be natural as a crystal, while its present color may nevertheless result from human intervention.
Examples include a natural diamond in which irradiation and annealing after mining created or redistributed vacancy centers.
The word natural must therefore always be tied to what it describes:
- natural diamond;
- natural color;
- natural inclusion;
- natural radiation stain.
One does not automatically prove the others.
Synthetic Diamonds: Color Produced During Growth
A synthetic diamond can incorporate impurities and defects during HPHT or CVD growth that already produce color at that stage.
Examples include:
- boron in blue HPHT or CVD diamonds;
- isolated nitrogen in some yellow HPHT diamonds;
- NV systems in some CVD populations.
Such color may be as-grown, but that does not mean “natural color” in the gemological sense. The material remains synthetic.
Post-Growth Color in a Synthetic Diamond
After growth, a synthetic stone may undergo additional processing to:
- reduce a brown component;
- intensify or change pink, blue, green, or another color;
- alter the population of vacancy and nitrogen-vacancy defects.
Growth method and post-growth treatment must therefore be separate fields.
The Same Color Center Can Exist in Different Histories
Boron, GR1, H3, and NV do not belong exclusively to a single origin.
For example:
- boron may exist in natural and synthetic diamond;
- GR1 may be produced by natural or artificial irradiation;
- H3 may be part of a natural history, but it can also appear after a treatment process;
- NV centers may exist in natural, treated, and synthetic material.
A laboratory therefore does not use the logic “we found X, so the stone is Y.”
The conclusion rests on a convergence of independent evidence.
An Integrated Laboratory Conclusion
Professional identification may combine:
- microscopy;
- diamond-type data;
- absorption spectroscopy;
- photoluminescence;
- luminescence imaging;
- zoning;
- fluorescence and phosphorescence;
- targeted additional methods.
Chapters 66–71 discuss the instruments in detail. The methodological point here is that no result should be interpreted outside the context of the complete sample.
Natural, Treated, and Undetermined Are Not Quality Levels
If a laboratory concludes:
- natural color;
- treated color;
- undetermined color origin;
this is not a “good–medium–bad” scale. These are epistemologically different conclusions about the origin of color.
Undetermined does not mean that treatment was found. It means that the available body of evidence does not allow possible pathways to be distinguished with sufficient confidence.
This is especially important with green diamonds.
A Surface Coating Is Not Body Color
A thin surface coating can alter the perception of the entire stone even though the internal volume has not acquired the same color-center system.
An examination therefore distinguishes:
- body color;
- surface color;
- reflection from the setting;
- contamination;
- fracture filler.
Fracture filling is likewise neither the “healing” of a fracture nor automatically a volumetric color treatment. It is a separate treatment and disclosure issue.
Current GIA Services for Natural Colored Diamonds
As of October 23, 2026, GIA publicly lists three principal services for natural colored diamonds:
- Colored Diamond Grading Report—a full quality assessment with a color grade and clarity plot, together with a conclusion on natural/treated color;
- Colored Diamond Origin Report—includes geographic origin, but requires a previously documented piece of rough in the GIA rough-analysis process;
- Colored Diamond Identification and Origin Report—an identification document for natural colored diamonds that describes the origin of color; also available for mounted stones within the scope of the service.
The word origin can therefore mean two different things: origin of color or geographic origin. The document must be read according to the full name of the service.
Current GIA Services for Synthetic Colored Diamonds
As of the same date, GIA separately lists:
- Synthetic Colored Diamond Report;
- Synthetic Colored Diamond Report – Color Identification.
These documents distinguish synthetic material from natural material and may include an assessment of growth type and post-growth treatment according to the scope of the specific service.
They should not be read as identical to natural colored reports simply because they share familiar words such as color or clarity.
CIBJO Nomenclature: The Rule Before and After Vicenza 2026
Until September 2026, the CIBJO Diamond Blue Book 2024-1 permitted the qualifiers synthetic, laboratory-grown, and laboratory-created for nonnatural diamonds, while requiring the product to be clearly distinguished from natural diamond.
On July 16, 2026, the CIBJO Diamond Commission published a Special Report proposing a preference for the term synthetic. At the Vicenza Congress, the CIBJO Board of Directors on September 7, 2026, approved the recommendation of the Diamond and Coloured Stone Commissions that “synthetic” be the sole descriptor in the Blue Books. As of October 23, 2026, the Diamond Blue Book 2026-1 requires that only the term “synthetic” be used for synthetic diamonds and does not permit words such as “grown,” “created,” or “cultured.” CIBJO acknowledges that “laboratory-grown” and “laboratory-created” are accepted consumer terms in certain jurisdictions and that national law takes precedence there (e.g., U.S.: FTC Jewelry Guides, 16 CFR Part 23).
This edition does not present the proposal to restrict the 4Cs to natural diamonds as adopted, because it is not confirmed by both the CIBJO press release and the text of the 2026-1 Blue Book.
There is an additional terminological boundary for treated natural diamonds. The current CIBJO Diamond Blue Book 2026-1 requires disclosure as treated diamond, with the type of treatment optionally added. According to CIBJO, the expressions natural treated diamond and treated natural diamond are not used because they may be misleading. This does not change the scientific fact that a laboratory must internally determine the natural origin of the crystal and subsequent treatment separately; it changes how the product is described in trade nomenclature.
This is an example of why a digital book must date regulatory and nomenclature claims.
Disclosure Is Not Evidence of Value
Proper disclosure of treatment and synthetic origin is necessary for fair trade, but it does not in itself determine price.
A laboratory report does not prove:
- purchase price;
- future resale price;
- ownership;
- legality of every prior transfer;
- ethical traceability;
- geographic mine, except when a specific origin service expressly covers it.
Practical Protocol for Reading a Colored-Diamond Report
- Determine whether the material is natural or synthetic.
- Read the full name of the laboratory service.
- Record the full color grade.
- Locate the separate conclusion on origin of color.
- If the diamond is synthetic, distinguish growth type from post-growth treatment.
- Check statements about additional treatments.
- Compare the weight, dimensions, plot, and inscription with the physical stone.
- Do not turn “origin” into geographic origin if the document addresses only origin of color.
- Do not turn a laboratory report into an appraisal or proof of ownership.
- For services that change over time, check the rules in effect on the document’s date.
Chapter Summary
- Material origin, origin of color, and additional treatment are three separate axes.
- A natural diamond can have treated color.
- A synthetic diamond can have as-grown or post-growth-modified color.
- Color grade describes appearance; origin of color describes the conclusion about how the color originated.
- Boron, GR1, H3, and NV may occur in several different natural, treated, and synthetic contexts.
- One spectral line is not sufficient for a final conclusion.
- Professional identification is based on an integrated body of evidence.
- “Undetermined” is not synonymous with “treated.”
- A surface coating, fracture filling, and body color are different phenomena.
- GIA currently has separate natural colored and synthetic colored services.
- On GIA documents, the word “origin” may denote origin of color or a geographic-origin service, depending on the full name of the report.
- Since the Diamond Blue Book 2026-1 (September 2026), CIBJO permits only the term synthetic for synthetic diamonds; national law (e.g., the FTC in the U.S.) may permit other qualifiers.
- Disclosure is required product information, but it is not an assessment of market value.
- Every document should be read according to the type of service and the rules in effect on its date of issue.
Sources for this chapter
Sources are primary or authoritative; the label in brackets gives the jurisdiction or source type.
- GIA: Colored Diamonds: Diamond Grading & Reports
- GIA: Natural Colored Diamond Reports & Services
- GIA: Diamond Treatments
- CIBJO: Fourth pre-congress Special Report (16 July 2026) (jurisdiction: international)
- CIBJO: CIBJO rules that ‘synthetic’ should be sole descriptor for created products with same chemical, physical and structural elements as natural equivalents (September 2026) (jurisdiction: international)
- CIBJO: Diamond Blue Book 2026-1 (jurisdiction: international)
- FTC: Jewelry Guides, 16 CFR Part 23 (jurisdiction: USA; federal guides)