DIY - zrób to sam

The polariscope may be one of the most underestimated tools in gemology. Most gemologists use it to quickly determine if the stone at hand is isotropic or anisotropic or, at best, to determine the optic character of gemstones. With some small additions, one can determine both optic character and the optic sign of a gemstone. It is also the preferred tool -- next to the microscope -- for separating synthetic amethyst from its natural counterparts (although with recent synthetics that may prove difficult).

https://www.jewelerstoolsmall.com/Gem-Polariscope-216.html

https://www.jewelerstoolsmall.com/goods-1554.html