In gemmological refractometry, gemstone refractometers determine the refractive index – physical abbreviation (n) – of cut stones via total internal reflection on the surface.
What exactly is measured? Due to their crystal structure and chemical composition, gemstones and precious stones have different optical properties, some of which can be determined with the gemstone refractometer. Refractometers are generally used to measure polished stones. It is only possible to measure rough stones if they have a perfectly flat crystal surface or if they have been ground or polished in one place beforehand. The devices allow direct determination of the specific light refraction of a stone, which is a characteristic feature. The specific value can be read directly from a visible scale in the refractometer.
The knowledgeable user also uses the device to determine information on birefringence for optical axes or optical orientation.
FUNCTION OF THE GEMSTONE REFRACTOMETER
For the investigation, a stone is placed in the refractometer on a small glass surface and illuminated at an angle from below. The reflected light beam is projected onto a scale, which can be viewed through the eyepiece of the refractometer. The refractive index determined is immediately recognizable by means of a cut-off line. The right illumination is essential for the cut-off line to appear sharp.
Ideally, no normal sunlight or lamp light is used, but monochromatic, i.e. monochromatic, light. This is usually yellow sodium light with the wavelength of the sodium D line, which is 589 nm.
Gemmological refractometry: refractive index measurement
Our premium gemstone refractometer impresses with brilliant optics and a bright, razor-sharp scale. It measures the refractive index of polished stones with the highest precision – indispensable for the reliable identification of gemstones, syntheses and imitations. Discover a sample examination and experience how the device is ready to use in just a few simple steps. You can find various refractometer models in the KRÜSS store.
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More InformationNote: The gemstone refractometer is also a central component of ourlarge mobile gemstone laboratory, which stands for maximum flexibility. Each of the two mobile gemmological laboratories is equipped with high-quality, professional analytical instruments and enables precise investigations on the move – at trade fairs, at customers’ premises or directly on site.
Want to read more?
If you are looking for more technical information, order the white paper “Gemstone refractometer”. The following examination methods are described in the specialist publication:
- Measurement of single-crushing stones
- Measurement of birefringent bricks with two cut-off lines
- Measurement of cut gemstones and precious stones
- Differentiation between emerald, spinel, glass and tourmaline
- Measurement of polished stones with a curved surface
- Example: Investigation using the “distant vision” method or “spot” method
- Measurement of rough stones with cut facets
The white paper was written in collaboration with Prof. Dr. Jochen Schlüter. He is a qualified mineralogist and is responsible for the display collection of the Mineralogical Museum in Hamburg.
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