Gak's Fotothing

A nice brown color is developed here where the crystals display nonspectral or unprismatic colors due to nonparalle refractive index dispersion curves. A polarizing filter splits light into two different polarized components which vibrate at 90 degrees from one another. So, they experience different refractive indices when they pass through the crystal. This means one ray is retarded relative to the other. When the two rays meet the analyzer filter, they split atain and two of the components become superposed on one another again. In other words, the two rays ar caused to recombine. But, their relative retardation means that their light waves will interfere, mor or less, depending on wavelength. Destructive inteference removes wavelengths so, the resulting light appears colored. If the refractive index change with wavelength (dispersion) of the two rays while they are in the crystal are not parallel, the final interference effect will be unbalanced, so nonspectral colors will appear, ones that cannot be seen in a rainbow. Colors like brown, purple, cyan and magenta may be seen.