corundum, color.4, gems, color science

While virtually all gemological texts cover pleochroism, it is almost always related to viewing with a dichroscope; exactly how pleochroism manifests itself in faceted gems is largely ignored. This article discusses this phenomenon in doubly refractive gemstones, specifically as it relates to overall color appearance in faceted gems. Contrary to popular belief, pleochroism can be visible in faceted gems even when they are cut with an optic axis parallel to the direction of view.