Gem Lab
Gemmological microscope
The most important instrument in the laboratory: under the microscope, inclusions, growth features and signs of treatment become visible.
No instrument is used as often in gemmology as the microscope. It reveals what remains hidden to the naked eye and often provides the decisive clues for further examination.
Design and function
The gemmological microscope is usually a stereo microscope with two eyepieces that produces a three-dimensional image. Typical magnifications range from about 10x to 80x. The stone is held in tweezers or a holder and can be rotated and tilted. An immersion cell, in which the stone rests in a liquid, reduces surface reflections and makes colour zoning more clearly visible.
Types of illumination
- Darkfield: light enters obliquely from below, inclusions light up against a dark background
- Brightfield: transmitted light shows colour distribution and outlines
- Reflected light: illuminates the surface, for example for polishing marks or fillings
- Fibre-optic light: targeted light on a single feature
What the microscope shows
Typical observations include crystal inclusions, fluid inclusions, healed fractures, rutile needles, growth lines and colour zoning. Treatments often leave characteristic traces: altered inclusions after heating, flash effects in filled fractures or gas bubbles in glass fillings. Synthetic stones sometimes show curved growth lines or flux residues.
The limits
The microscope provides observations, not proof for every question. Origin determination or the detection of certain treatments also require spectroscopic and chemical methods. Some stones are so clean that hardly any features are present. Interpretation requires experience and reference material.
In brief
The microscope is the first and most important tool of an examination. It reveals inclusions, growth features and signs of treatment and guides further measurements. For origin and many treatments, spectroscopic and chemical methods are also needed.
At NOBILITH
In the Academy masterclasses, the virtual microscope shows three typical features for each species. These are illustrations, not images of specific stones; they help to understand descriptions in laboratory reports. The findings for a particular stone are in the laboratory's report.
Sources
- Gübelin, E. and Koivula, J.: Photoatlas of Inclusions in Gemstones
- GIA: Gem Encyclopedia, gemmological microscope
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 LabRefractometerThe refractometer measures how strongly a stone bends light. This allows many materials to be narrowed down quickly – within clear limits.Read more
- Gem LabPolariscopeBetween two crossed polarising filters a stone reveals how it refracts light. A simple instrument with meaningful results.Read more
Updated 2026-10-06