The colour red has long been associated with fire and passion, and the ruby is no exception. Ancient Sanskrit texts refer to the ruby as ratnaraj, or King of Gemstones, and legends from around the world speak of kings and queens of eras past who adorned themselves with fiery red rubies.

Characteristics
The ruby is a variety of the mineral corundum that contains aluminium oxide impurities. The characteristic feature of corundum is the hardness of the mineral, leading to extremely resilient gems. The ruby is one of the hardest gemstones to be found, second only to the diamond, and is rated 9 on the Mohs scale of hardness.

Pure corundum is a colourless mineral and derives its colour from trace impurities present in it. While corundum of all other colours is designated as sapphire, red corundum has the unique distinction of being a different type of gemstone. Rubies derive their colour from chromium present in the corundum. The colour of the ruby will be more intense as the amount of chromium in the corundum increases. A ruby varies in translucency, ranging from transparent to completely opaque, and the value of a transparent ruby is higher than that of an opaque gem.

Certain rubies can sometimes display a star-like effect or an asterism. These rubies contain needle-shape rutile-like inclusions, referred to as silk, that create the illusion of a six-rayed star inside the ruby. The asteriated effect is clearest in a ruby that is cut as a half-dome shaped cabochon, and is more clearly seen in semi-transparent to opaque rubies.

Gem Mines of Burma: Rubies and Controversy
The best rubies of the world are found in the mines of Burma, or Myanmar. The premier Burmese ruby mines are the Mogok and Mong Hsu mines, while other smaller mines include Nawarat, Nayaseik, Katpana and Sangyin. Burmese rubies are considered the most valuable in the world.

The Mogok stone tract lies at 4,000 feet above sea level in the Mogok Valley in Burma and has yielded some of the world's finest rubies. The name "Mogok" comes from the Burmese word Bamar Moegokesetwaing, meaning horizon, and the Mogok Valley contains over 1,000 ruby and sapphire mines.

Mogok rubies tend to be well formed, rounded rubies that may contain patches, zoning or overall cloudiness created by short, fine rutile needles or silk inclusions. These rubies contain a strong red fluorescence and are often nearer in colour to magenta.

Mong Hsu rubies are easily differentiated from Mogok rubies, primarily because they often have a bluish hue or core in the stone. Mong Hsu rubies also contain healing feathers, several distinct growth zoning patterns, and very fine white needles on inclusions in untreated stones. Nearly all Mong Hsu rubies are subjected to heat treatment to remove the bluish hue and improve the red colour of the stone. Most of the treatment to Möng Hsu rubies is undertaken in Thailand.

Pigeon's Blood: The Burmese word for ruby, padamya, means "plenty of mercury" after their distinctive red tone, but the term ko twe, or "pigeon's blood", is used to refer to rubies of the finest shade of red. These rubies are so termed because their deep red hue resembles that of freshly drawn arterial pigeon's blood. True pigeon's blood rubies are extremely rare.

Ban on Burmese Rubies: Human rights and political groups around the world have been vociferously objecting to the import of Burmese rubies for years, and governments are now taking action based on their evidence. In Burma, which has been under military regime since 1962, the majority of gem mines and trading operations are controlled by the junta. While the exact figure is unknown, it is alleged that the junta makes 300 to 400 million dollars a year from the export of rubies. The mines are prohibited to outsiders, and the conditions of the workmen are said to be horrifying.

As a consequence, the International Colored Gemstone Association in 2007 urged its members to stop buying Burmese gemstones from government sources. However, the ICA has not recommended imposition of a sweeping ban of trade of Burmese gemstones for fear of such a ban causing severe damage to the non-governmental parties engaged in mining.

The United States of America has not been as liberal. It first imposed a ban on import of rough gems from Burma in 2003, but the legislation had a severe flaw. Burmese gemstones are faceted and treated outside Burma, and the legislation did not prevent the import of Burmese gems via other countries. Any strict ban on import of Burmese gems was usually self-imposed by merchants and jewellers. In July 2008, President George W. Bush signed new legislation that bans import of Burmese rubies and jadeite even if the stones were to enter the US from a third country, with or without "substantial transformation". The US amended its previous legislation on the belief that Burma was evading sanctions by laundering the stones in other countries before export into the US. However the legislation does not ban the import of Burmese stones for personal use, nor does it prevent sale of the stones that are already in the country at the time of enactment.

Burmese gem traders are not impressed by this ban. Ninety per cent of the world's rubies are produced in Burma, and the majority of their buyers come from China, Russia, the Gulf, India, Thailand, and the European Union. Burmese jewellers and traders are of the opinion that the US ban on import of their gems is not likely to substantially affect their business.

Other Asian Mines
The Jegdalek mines in Afghanistan are the primary corundum mines in the region, yielding both rubies and sapphires. The mines have produced beautiful rubies for over 700 years and are located 100 kilometres east of Kabul in a region that is nearly inaccessible due to its natural terrain.

Jegdalek rubies come in a variety of hues, from nearly colourless to deep red to purplish-red, displaying strong fluorescence in ultraviolet radiation. Approximately 15% of the stones mined in this region are rubies. Most of the mines' gem production is transported to Peshawat in Pakistan through the Khyber Pass.

Enhancements
Heat Treatment: Rubies have long been exposed to heat treatment to improve their red colour and remove any secondary colours. Heat treatment is done using a combination of chemicals such as beryllium, borax, lead, and tantalum, and the ruby is subjected to temperatures ranging from 1500 to 1850 degrees Celsius for several hours.

Most Mong Hsu rubies, which have bluish undertones, are heat-treated to remove the blue and improve the red colour of the stone. Rubies that are so enhanced may often develop fractures, decrepitation feathers or rutile needles as a result of the stress of heat treatment, and must then be further treated to mask these flaws. A ruby that shows no signs of heating is very rare and must be certified to determine its value.

Flux Healing: The flux healing method of enhancement is used to repair surface cracks, inclusions or cavities that may be present in a ruby. In flux healing, the ruby is exposed to a combination of heat and solvents, such as borax and other fluxes, to fill any imperfections with a mixture of what is known as molten low-viscosity flux glass. The mixture dissolves the walls of the fracture until the liquid becomes saturated with molten ruby solution. As the mixture cools, it will permanently fuse the fracture. Flux healing reduces internal reflections, thereby making the ruby seem more transparent.

Corundum Diffusion: Corundum diffusion is also known as Lattice Diffusion or Deep Diffusion. This process involves the use of diffusion to introduce colouring elements, such as beryllium, into the corundum to fill any possible voids in the crystal lattice structure. The use of corundum diffusion is considered unethical as it is difficult to detect and it therefore becomes easy to mislead a buyer and may also affect the authentic valuation of treated ruby.

Famous Rubies
Carmen Lúcia Ruby: Mined in the Mogok Valley in the 1930s, the Carmen Lúcia Ruby is one the largest faceted Burmese rubies in existence. Displayed in the Smithsonian National Museum of Natural History, the ruby weighs 23.10 carats, a size which is exceedingly rare for a Burmese ruby of such exceptional quality as the Carmen Lúcia. The gem displays a rich red colour and is of extraordinary transparency. The Carmen Lúcia Ruby was donated to the National Gem Collection of the Smithsonian Museum by Dr. Peter Buck in memory of his wife Carmen Lúcia Buck.

Rosser Reeves Star Ruby: Named after its owner who donated the ruby to the Smithsonian Museum, the Rosser Reeves Star Ruby is a 138.7 carat ruby that originated in Sri Lanka and is reputed to be the largest and finest star ruby known. The stone bears a magnificent shade of red and a sharp six-rayed star. Mr. and Mrs. Rosser Reeves donated the ruby to the Museum in 1965, where it has been in display ever since.

Delong Star Ruby: Weighing 100.32 carats, the Delong Star Ruby is part of the permanent collection of the American Museum of Natural History in New York. The stone was discovered in Burma and donated to the Museum in 1937 by Martin Ehrmann, from where it was stolen along with the Star of India sapphire in an infamous heist in 1964. The Delong Star was recovered at a designated drop off site after a ransom of US $25,000 was paid.

Nga Mauk and Kallahpyan Rubies: During the mid-1800s, a 560 carat ruby was found in the Burmese Mogok mines that today boasts an enthralling legend. The stone's owner broke it in two and gifted one half to King Mindon Min. The other half is believed to have been secretly sent to Calcutta to be sold. When Mindon Min discovered that he had been presented with only half of a marvellous ruby, he ordered that the other half be returned to him and that the village and its inhabitants be burned alive as a punishment and a deterrent to others. The other half was purchased from Calcutta and returned to Burma. The two stones were cut into the Nga Mauk and Kallahpyan rubies, weighing 98 carats and 74 carats respectively. The rubies' whereabouts have been unknown since 1885 when the British annexed Upper Burma.