Testing gemstones with dichroscopes

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

Dichroscopes reveal whether transparent, coloured gemstones exhibit pleochroism, i.e. direction-dependent polychromatism. As a result, these devices can be used to test gemstones and often differentiate natural stones from one another and identify imitations. Numerous natural stones have a characteristic pleochroism and can be identified by it.

Different colours or hues of the stone to be examined can be seen when looking into the dichroscope and if pleochroism is present. 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. For the majority of colored stones, however, it is not possible to test gemstones with the naked eye, as they only show weak pleochroism. Different devices can be used to determine this characteristics, for example the polariscope or the dichroscope. The examination method is relatively simple.

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Gemmologie Exklusiv Tipp

Rapid detection of the green tourmaline with the dichroscope

The dichroscope is also an important auxiliary tool. In this device inside, light emanating from the stone to be examined is broken down by a calcite crystal into two adjacent light beams polarised perpendicular to each other.

In our example, the green light from a green tourmaline falling into the dichroscope. Here it is separated into a northsouth oscillating and an east-west oscillating light beam. Since the two beams were absorbed differently in the tourmaline due to their different oscillation directions, one appears in green and the other in a blue-green colour. Weak pleochroism is very often difficult to recognise in faceted stones, which is why we recommend viewing them with an immersion liquid – it is often sufficient enough to place the stone in a glass vessel filled with water. A colored stone that does not show pleochroism is either isotropic, e.g. garnet, or amorphous, e.g. glass. 

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.

Do you want to read more?

Here you can order the free white paper “Dichroscopes”, in which many pleochroism examinations are described. 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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