Ruby is from the Latin word for red and is found in various shades of purplish, pinkish, orangey and brownish-red as well as the rare pure red colour. They often show good fluorescence in sunlight and incandescent light. The finest rubies are described as pigeon blood red and when they also possess good clarity, they are deemed very rare and exceed the price of diamonds carat for carat.
The most prized rubies came from deposits in the Magok area of Burma (now Myanmar) recently reported as mined-out. Rubies are mined in other areas of Myanmar and are still referred to as Burma ruby.
The largest known ruby in the world is the 'Liberty Bell' at 8,500 carats (4 pounds). Unfortunately it was stolen form a jewellery store in Delaware, USA in 2011 with little hope of it being recovered.
Most of the larger fine rubies are held in private collections, typically purchased in auctions for very high prices.
Over the ages rubies were set into Royal Regalia (Crown Jewels) including crowns, swords, rings and other jewellery items. Some of the stones thought to be ruby were in fact Red Spinel a gemstone easily confused with ruby. New gemmological tests proved those stones to have single refraction and belonging to the cubic crystal system (isotropic). Ruby belongs to the trigonal crystal system (anisotropic) and has double refraction.
Rubellite (red tourmaline) is a very attractive gemstone, also similar in colour to ruby, from which it takes it's name. Good examples could easily be mistaken for ruby.
Ruby is one of only two varieties of the species corundum, the other variety is sapphire which occurs in all colours except red. It is often difficult to differentiate between a ruby and some pink sapphire. There is no precise demarcation between colours and the human memory is poor at retaining precise colours, without reference colours at hand. Different types of lighting can also affect the perceived colour of ruby drastically, hence some borderline pink sapphires have been sold as a rubies.
When used in jewellery ruby and sapphire are not prone to damage, at 9 on the Mohs' scale of hardness they are very hard and durable gemstones. Diamond is the only naturally occurring material harder than corundum (ruby and sapphire).
Source locations for ruby include: Afghanistan, Australia, Brazil, Cambodia, Madagascar, Myanmar, Pakistan, Thailand and the USA.
Heat treatment is commonly used to improve the colour of ruby and also it's transparency by dissolving rutile inclusions, known as silk. The rubies are placed in custom made ovens and 'cooked' at high temperatures for many hours or even days, then cooled rapidly. Following treatment the colour remains stable, but heavily included stones may be weakened by the heating process.
Surface reaching cavities may be filled with lead glass or other materials.
Oiling of cracked stones is carried out to reduce the visibility of the cracks, improving the clarity, colour and therefore general appearance of the stone.
Surface or lattice diffusion of corundum is carried out on pale or near colourless stones of low value. This process applies a layer of colour that just penetrates the stones surface. The treated stone may appear as an incredibly fine example of ruby, but re-polishing these stones with abrasive wheels will remove the skin-deep layer thereby removing the colour. Any chipping to the facets, although unlikely, would also show a change of colour.
Beryllium diffusion of corundum is a new concept in ruby and sapphire enhancement. The process creates yellow, orange, red, brown and blue colours from pale or nearly colourless material. It can also change an actual colour and transform dull coloured corundum into vibrant richly coloured material. For example, bluish rubies after diffusion may be a fine red colour. Beryllium diffusion may colour an area close to the surface or may penetrate the entire stone.