Ruby Buying Guide
Rubies are the gemstone variety of red corundum, the same mineral that is sapphire in any other colour. As such, they have a hardness equal to that of sapphires (9) and their resistance to chipping and scratching makes them the ideal choice for use in engagement rings and other jewellery. Rubies are one of the most expensive gemstones available today and are mined in Sri Lanka, Myanmar (Burma), Thailand, Vietnam, China, Afghanistan, Kenya and Tanzania.
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.
A ruby owes its colour to the presence of chromium in its chemical composition and increased amounts of chromium lead to increased colour intensity. The intensity of the red colour is the primary factor determining the value of a ruby. The saturation, tone and hue of a ruby should all be taken into account when looking for the ideal stone. Saturation is the brightness or vividness of colour in a ruby and tone refers to the lightness or darkness of a ruby.
The ideal ruby colour is known as “Pigeon blood” and is typically found in rubies originating from Burma, but is now also found in Mozambican rubies.
Rubies tend to be less clean relative to sapphires. As with all gemstones, inclusions in a ruby indicate the authenticity of the stone and may be used to uniquely identify it. Although increased amounts of chromium in a ruby lead to brighter and more intense red colours, it also leads to a decrease in clarity due to the generation of fractures and inclusions within the stone. A flawless (i.e. inclusion-free) ruby is exceptionally rare and as such can command premium prices. Rubies available in jewellery market places tend to be slightly included at the very least.
The majority of rubies on sale today have been subjected to heat treatment to enhance their appearance and colour. This process is permanent and a treated ruby will not diminish in colour, saturation or hue over time. Many rubies are also heated in the presence of a flux which heals their fractures, thus improving their clarity. Untreated rubies are hard to come by and an authentic, untreated ruby may cost 50% more than it’s treated equal.