Gem Lab
Spectroscope
The hand spectroscope splits the light passing through a stone and shows dark absorption lines – often a clue to colour-causing elements.
Colour arises because a stone absorbs certain parts of light. The hand spectroscope makes this absorption visible. It is small, quick and non-destructive, and in experienced hands it provides valuable clues.
How it works
White light is directed through the stone or from its surface into the spectroscope. A prism or diffraction grating spreads it into a band from violet to red. Where the stone absorbs light, dark lines or bands appear. Their position and shape are typical of particular elements.
Typical patterns
- Chromium: fine lines in the red and a broad band in the yellow-green, for example in ruby, emerald or alexandrite
- Iron: lines in the blue, characteristic of many blue and green sapphires
- Cobalt: three broad bands, typical of cobalt-coloured glass and synthetic blue spinel
- Rare earth elements: sharp lines, for example in some apatites
Such patterns can support an identification or raise a suspicion, for example when a supposed sapphire shows a cobalt spectrum.
The limits
Many stones show only weak lines or none at all. The observation is subjective and depends on the light source, the size of the stone and experience. Overlapping patterns are difficult to separate. The hand spectroscope therefore does not replace the instrumental spectroscopy that laboratories perform with UV-Vis-NIR equipment.
Use today
In modern laboratories the hand spectroscope serves mainly as a quick preliminary test and for training. Reliable data come from spectrometers that measure and record absorption over a wide range of wavelengths.
In brief
The hand spectroscope shows absorption lines that point to colour-causing elements. It is quick and non-destructive, but subjective and limited with weak patterns. Reliable data today come from instrumental spectrometers that measure absorption over a wide range.
At NOBILITH
Understanding the basics of the hand spectroscope also helps in understanding the instrumental methods mentioned in laboratory reports. The Academy presents these methods in separate articles.
Sources
- GIA: Gem Encyclopedia, spectroscope
- Anderson, B. W.: Gem Testing
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