Iceland stone table rotating dichroic mirror -- FABLE
When natural light enters the inhomogeneous gemstone, it is decomposed into two beams of polarized light whose directions of vibration are perpendicular to each other. The anisotropy of an inhomogeneous gem causes the stone to absorb light in different vibrational directions differently, and it is possible to see different colors as long as the light from the two vibrational directions can be separated. The commonly used dichroic mirror is the Iceland SPAR dichroic mirror, which is composed of glass prism, Iceland SPAR prism, lens, light window and eyepiece. Iceland SPAR has a very strong birefringence with a birefringence index of 0.172 (No = 1.658, Ne = 1.486), which can decompose a beam of light into two polarized rays. The length of the Iceland ridge is designed to make the two images of the hole appear side by side in the eyepiece. When a multicolor gem is observed, the Iceland SPAR dichroscope again disassembles the two beams of polarized color light that pass through the gem, allowing the colors of the two polarized beams to appear side by side in the two effects of the window. Homoplast gems do not have anisotropy, so there is no polychromatism, and the observed two Windows have the same color. Heterogeneous colored gems have anisotropy and thus have polychromatism. The true multicolor color of the stone is seen only when the directions of the two polarized light beams passing through the gem are parallel or perpendicular to each other and to the principal axis of the light rate of the Iceland ridge. If the vibrational direction of the light passing through the gem intersects the optical axis of the surface of the Iceland prism at 45 °, the polychromatism cannot be seen. This is why the color of the second window keeps changing as you rotate the dichroic mirror and the gem. It should be pointed out that when the optical axis of the inhomogeneous colored gem is parallel to the long axis of the dichroic mirror, the polychromatism cannot be seen.
Purpose:
Helps identify stones with strong polychromatic properties; Such as: cordierite tricolour is significant (blue, violet blue, light yellow).
Distinguish between isotropic and anisotropic gems; Ruby and red spinel.
Understanding the polychromatism of gemstones is very helpful to the orientation of cutting and grinding gemstones. Such as ruby in the processing of the top cut surface should be vertical axis direction, in order to show the best color of the stone through the top cut surface.