gems, corundum, color.4

The phenomenon of pleochroism in doubly refractive (DR) gemstones is described, as it relates to overall color appearance in the context of faceted gems. With strongly pleochroic gems, pleochroism can be seen in faceted gems, even if the table facet is oriented perpendicular to an optic axis. This is because facets change the direction of light as it moves through the gem.