Identification and Screening
The greatest practical mistake in modern gemology would be to expect one rapid test that reliably classifies every diamond as natural, HPHT-grown, or CVD-grown. No such universal test exists.
A professional system must distinguish material verification, origin screening, final origin identification, and treatment identification.
First Question: Is It Diamond?
Thermal conductivity, electrical properties, optical observation, and Raman can help confirm diamond material or separate simulants. Once a sample has been confirmed as diamond, however, an ordinary handheld diamond tester is generally insufficient to answer whether the crystal is natural or synthetic (laboratory-grown).
This is why the simulant testing in Chapters 64–65 must not be conflated with origin screening.
Screening Is Not Final Identification
Screening is triage. Its purpose is to separate quickly the samples that satisfy a system’s validated criteria from those requiring further analysis.
An instrument may use categories such as pass, refer, test again, fail, or out of scope, but the meanings of these terms are not universal. They must be read according to the documentation for the specific model, software version, size range, shapes, colors, and stone-placement method.
In particular:
- pass usually means that the sample met the criteria for passing within the validated scope;
- refer means that the device could not classify it safely and that further analysis is required;
- refer is not synonymous with synthetic;
- out of scope means that the sample does not fall within the method’s validated scope, not that it is “suspicious.”
Loose, Mounted, and Melee Require Different Protocols
A loose stone provides access to every facet and allows its position to be standardized most easily. A mounted stone may be partly obscured by metal, contaminated, or inaccessible to certain measurement geometries. Melee parcels introduce the problems of a large number of samples, different orientations, and possible mixing of categories.
A result from a system validated for a defined size range of loose round stones must therefore not be extended automatically to mounted melee or rough.
Microscopy: Useful, but Not Final
A microscope may reveal metallic growth remnants, specific zoning, graphitic pinpoints, layers, fractures, or other features that support a particular hypothesis. Modern HPHT and CVD material, however, may be so clean that it shows none of the classic features.
Conversely, a natural diamond may contain metallic or graphitic phases and complex strain patterns. “I saw metal,” “I saw black spots,” or “I saw bands” are therefore insufficient as final statements.
Strain and Luminescence
Crossed polarizers provide information about anomalous birefringence and strain. Deep-UV imaging can reveal growth sectors and growth striations. In classic HPHT populations, a sectoral luminescence architecture is often visible; CVD often displays layers and bands associated with growth.
Technological development, however, increases overlap. In 2024, GIA documented CVD diamonds whose deep-UV images could appear similar to those of some natural samples. An image must therefore always be connected with spectroscopy.
FTIR: A Powerful Screening Layer, Not a Verdict
FTIR determines atomic type and part of the defect chemistry. GIA’s 2024 review of synthetic populations states that colorless-to-near-colorless synthetic diamonds are type II, whereas type II forms only a very small population among natural diamonds—approximately 1% in the cited GIA literature.
This makes a type II finding a strong reason for additional analysis, but type II is not the same as synthetic. Natural type IIa and IIb diamonds exist and may be gemologically very important. This population relationship serves screening, not binary identification of an individual stone.
UV-Vis-NIR, Raman, and PL
UV-Vis-NIR helps characterize absorption systems associated with color and treatment. Raman confirms diamond and can identify certain inclusions. Photoluminescence is especially sensitive to low concentrations of defects and can be measured using different excitation wavelengths and temperatures.
Centers such as NV, SiV, H3, nickel-related emissions, and others can strongly support an interpretation, but they must not be turned into simple binary tests. GIA’s 2024 analysis specifically cautions that SiV is not detected in every CVD diamond and may occasionally occur in natural diamonds as well.
Combined Identification
A reliable conclusion about origin emerges when multiple independent layers of data point in the same direction. A CVD interpretation might include a layered growth pattern under deep-UV excitation, an appropriate FTIR type, a PL assemblage compatible with CVD growth, and other consistent characteristics. An HPHT interpretation might combine a sectoral growth pattern, appropriate growth remnants, atomic type, and spectroscopic findings.
No single layer is required in every case. This is precisely why major laboratories maintain reference databases of natural, treated, and synthetic diamonds and adapt their workflows to new products.
Post-Growth Treatment Increases Overlap
HPHT annealing of a CVD diamond can remove some as-grown centers, create or strengthen others, and alter the luminescence appearance. Irradiation and annealing can further change the spectrum. Identification must therefore answer two separate questions: how the diamond grew and what happened to it after growth.
Documentation Is Not Analytics
A laser inscription and digital report check are useful layers of traceability, but an inscription may be removed, altered, or counterfeited. The existence of an online report proves that a record exists, not that the stone in hand is physically the same specimen.
Physical matching requires comparison of weight, dimensions, inscription, clarity characteristics, and other identification elements.
Professional Multilevel Workflow
- Define the question: simulant, natural/LGD screening, growth method, or treatment.
- Record and clean the sample.
- Confirm diamond material when necessary.
- Apply screening only within the device’s declared scope.
- Send a refer result for expanded analysis rather than declaring the stone synthetic.
- Document microscopy, strain, and luminescence.
- Determine atomic type by FTIR when relevant.
- Add UV-Vis-NIR and PL according to the hypothesis.
- Analyze growth origin and post-growth treatment separately.
- Compare the findings with validated reference data.
- Check the report and physical match if a document exists.
- Conclude only what the combined evidence supports.
If the data remain contradictory or insufficient, a professional result may be undetermined / additional testing required.
Chapter Summary
- Material identification and growth-origin identification are different tasks.
- An ordinary diamond tester generally does not resolve natural versus synthetic origin.
- Screening is triage, not final identification.
- Pass, refer, and out-of-scope have meaning only within the documentation of the specific system.
- Refer does not mean synthetic.
- Loose, mounted, melee, and rough require different validated protocols.
- Microscopic features may be indicative but are rarely universally diagnostic.
- A type II finding is a strong reason for additional analysis but is not proof of synthetic origin.
- Deep-UV growth patterns are highly useful but must be connected with spectroscopy.
- SiV is not a stand-alone CVD test.
- Post-growth treatment can obscure or alter original growth signals.
- The final conclusion rests on the convergence of multiple independent findings.
Sources for this chapter
Sources are primary or authoritative; the label in brackets gives the jurisdiction or source type.
- GIA / G&G: Laboratory-Grown Diamonds: An Update on Identification and Products Evaluated at GIA (Summer 2024)
- GIA / G&G: Separation of Natural from Laboratory-Grown Diamond Using Time-Gated Luminescence Imaging (Summer 2020)
- GIA / G&G: Eaton-Magaña & Shigley 2016, Observations on CVD-Grown Synthetic Diamonds: A Review