Gem Lab
UV-Vis-NIR spectroscopy
The spectrometer measures which wavelengths a stone absorbs from the ultraviolet to the near infrared. The curve explains colour and offers clues to treatments.
UV-Vis-NIR spectroscopy is the instrumental development of the hand spectroscope. Instead of judging lines by eye, a spectrometer measures absorption across a wide range and records it as a curve.
The measuring range
Measurement extends from the ultraviolet (about 250–400 nanometres) through visible light (about 400–700 nanometres) into the near infrared (about 700–1100 nanometres or beyond). This captures absorptions that the eye cannot see but that are important for interpretation.
What the curve reveals
- Cause of colour: chromium, iron, titanium, vanadium or copper produce typical absorption bands
- Treatment: heating can alter certain bands, for example in sapphire
- Variety: absorption helps to clarify whether a colour meets the criteria for a name, for example copper-related colour in Paraíba tourmaline
- Diamonds: nitrogen and defect centres give clues to type and possible treatments
Polarised measurement
Many gemstones absorb differently depending on direction; they are pleochroic. Laboratories therefore often measure with polarised light in a defined orientation so that spectra become comparable.
The limits
The value of the method depends on reference data. A spectrum alone rarely determines origin; for that it is combined with inclusions and trace elements. Large or very dark stones let little light through, thin stones give weak signals. Interpretation requires experienced specialists.
A strength of the method
The measurement is non-destructive and can be documented: the spectrum is stored and can be compared again later, even when new reference data become available.
In brief
UV-Vis-NIR spectroscopy measures absorption from the ultraviolet into the near infrared. It explains causes of colour and supports statements on treatment and variety. Its value depends on reference data and grows in combination with other methods.
At NOBILITH
Laboratory reports do not always list the methods used in detail. Where a treatment or origin statement is given, leading laboratories generally base it partly on spectroscopic measurements such as this. The Academy explains what the method can and cannot do.
Sources
- GIA: Gems & Gemology, articles on UV-Vis-NIR spectroscopy
- LMHC: Information Sheets
Read more
- Laboratory reportsUnderstanding a laboratory reportA laboratory report is a gemstone's most important document. Which information it contains, how to read it and what it does not say.Read more
- KnowledgeWhy a laboratory may say inconclusiveSometimes a question cannot be answered responsibly with the available data. What “inconclusive” means – and what it does not.Read more
- Gem LabGemmological microscopeThe most important instrument in the laboratory: under the microscope, inclusions, growth features and signs of treatment become visible.Read more
- Gem LabRefractometerThe refractometer measures how strongly a stone bends light. This allows many materials to be narrowed down quickly – within clear limits.Read more
Updated 2026-10-06