Testing gemstones with dichroscopes

Here’s how you can test gemstones and spot imitations:

Dichroscopes can detect whether transparent, colored gemstones have pleochroism, i.e. direction-dependent polychromy. This means that these devices can be used to test gemstones and in many cases distinguish between natural stones and identify imitations. Numerous natural stones have a characteristic pleochroism and can be identified by it.

When looking into the dichroscope and if pleochroism is present, different colors or shades of the stone under investigation are revealed. In this way you can test your gemstone and distinguish it from imitations or fakes. Strong pleochroism, such as in the case of ornamental stones cordierite or tanzanite, can also be seen with the naked eye in non-polarised light. With the majority of the colored stones, however, the detection of pleochroism is not possible, since they only show a weak pleochroism. Various devices can be used to determine this property, e.g. the polariscope or the dichroscope. The investigation is relatively simple.

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Rapid detection of the green tourmaline with the dichroscope

The dichroscope is also an important auxiliary tool. In this device, the light coming from the stone to be tested is split inside by a calcite crystal into two adjacent and perpendicularly polarised light beams.

In our example, green light from a green tourmaline falls into the dichroscope. Here it is separated into a northsouth oscillating and an east-west oscillating light beam. As the two rays were absorbed differently in the tourmaline due to their different vibrational directions, one appears in green and the other in blue-green color. Weak pleochroism is often difficult to recognize in faceted stones, so it is recommended to view them with the help of an immersion liquid – it is often sufficient to place the stone in a glass vessel filled with water. A colored stone that shows no pleochroism is either isotropic, e.g. garnet, or amorphous, e.g. glass.

Testing gemstones with pleochroism analysis

Experience how the dichroscope, in combination with a cold light source, enables fast and precise gemstone identification – and helps to separate genuine natural stones from deceptively similar imitations. You can find various dichroscope models in the KRÜSS store.

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Note: The hand-held dichroscope 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?

There are many other manifestations in the observing of pleochroism. We have compiled a large selection of relevant specialist information with many interesting detailed photos on dichroscopy in the free white paper “Dichroscopes”. This specialist publication 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.

Here you can order the free white paper “Dichroscopes”, which describes many pleochroism investigations. Simply enter your contact details here and we will send you our detailed white paper as a PDF on the subject of “dichroscopes” by email.

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