Polariscopy enables the rapid identification of common gemstone imitations, such as glasses or synthetic spinels. This is done by investigating the optical properties of the stones with polarized light. With the polariscope, it is possible to investigate both cut and rough stones. Depending on the size of the polarisers, it is even possible to investigate several stones at the same time.
How is the investigation carried out? To view precious stones and gemstones – but also syntheses or imitations – these are placed on the rotatable glass plate and positioned above the polariser. In this way, the materials to be investigated are positioned between the polariser and the analyser. Illumination is from below and the materials are viewed from above.
How the polariscope works
The propagating light oscillates in all directions perpendicular to the direction of propagation. When passing through a polariser, only one direction of oscillation is maintained. If the polariser and analyser are rotated exactly 90° against each other for the dark position, the background of the stones is black. This is the dark position (figure polariscope left).
What can you see? Glass stones very often have internal stresses and then show anomalous anisotropy (direction-dependent properties). This means that they develop bright areas when viewed through a polariscope. Dark bars that move through the stone when it is rotated are also typical of glass stones (middle image). Synthetic spinels produced using the Verneuil process also show anomalous stress birefringence. As cubic substances, they should remain dark when rotated under crossed polarisers. However, the characteristic appearance of the synthetic spinels, the spindle-like brightenings, become visible under the polariser and reveal them immediately (figure on the far right).
How the polariscope analyzes imitations
See how easy the Polariscope is to set up and use in practice: The device immediately shows the optical behavior of the stone. Whether polished or rough – even several stones can be examined at the same time. Various polariscope models are available in the KRÜSS store for gemmology.
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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.
Do you want to read more?
If you are looking for more specialist information, order the white paper “Gemstone polariscopy”. The following topics, for example, are described in the specialist publication:
- Design and mode of operation of a polariscope
- Demonstration of light position and dark position
- Differentiation of ruby, red spinel, red garnet, tourmaline
- Determine gemstone imitations such as glass or synthetic spinels
- Viewing faceted red stones between crossed polarisers in dark position
- Viewing faceted stones embedded in immersion liquid
- Determine axial images of e.g. amethyst with an additional conoscopic lens
The whitepaper was produced in collaboration with Prof. Dr. Jochen Schlueter wrote. a qualified mineralogist in charge of the permanent collection on display at the Mineralogical Museum in Hamburg.
Simply enter your contact details here and we will send you our detailed whitepaper as a PDF file on “Polariscopy” by e-mail.