The polariscope/conoscope consists of two polarising filters arranged perpendicular to one other. It makes it possible to identify the otic character of the gemstone, directly linked to its crystalline structure (Isotropic or Anisotropic).
Coupled with a conoscope, which is a glass bead without internal flaws, it can determine the number of optical axes (uniaxial or biaxial) in optically anisotropic gems.