Like all gemstones, the cut of a ruby is determined by the crystal shape of the rough ruby. As a result, oval and cushion cut rubies are two of the most common cuts found in the market place, and while cuts such as round, marquise, emerald and pear cuts are all available they are almost always hard to find in larger carat sizes. Because rough ruby is expensive, cutters will try to maximise as much of the stone weight as possible and, as a result, sometimes cut poorly-proportioned shallow stones. In these instances, light escapes through flattened pavilions in the stone, leading to a see-through area known as a “window”.
Rubies also exhibit a feature known as pleochroism, where different colours are exhibited in different crystal directions. In one direction rubies can appear red to purplish-red, while in another direction the colour is more orangey-red. The direction that a ruby is cut in therefore has a direct impact on the final colour of the gem.