A polariscope is used to differentiate between singly (isotropic) and doubly refractive (anisotropic) stones. A stone is placed between two polarizing filters and the top filter is then turned. If used with a conoscope, interference figures can also be seen with a polariscope. Conoscopes are difficult to explain in words, so directions for use are not covered here. We suggest you consult http://www.gemologyproject.com. They have videos showing the use of the conoscope.