Rubies

Prices of rubies are primarily determined by color. The brightest and best "red" called pigeon blood red, commands a huge premium over other rubies of similar quality. After color follows clarity: similar to diamonds, a clear stone will command a premium, but a ruby without any needle-like rutile inclusions will indicate the stone has been treated one way or another. Cut and carat (size) also determine the price.

Physical properties

Rubies have a hardness of 9.0 on the Mohs scale of mineral hardness. Among the natural gems only moissanite and diamond are harder, with diamond having a Mohs hardness of 10.0 and moissonite falling somewhere in between corundum (ruby) and diamond in hardness.

All natural rubies have imperfections in them, including color impurities and inclusions of rutile needles known as "silk". Gemologists use these needle inclusions found in natural rubies to distinguish them from synthetics, simulants, or substitutes. Usually the rough stone is heated before cutting. Almost all rubies today are treated in some form, with heat treatment being the most common practice. However, rubies that are completely untreated but still of excellent quality command a large premium.

Some rubies show a 3-point or 6-point asterism or star. These rubies are cut into cabochons to display the effect properly. Asterisms are best visible with a single-light source, and move across the stone as the light moves or the stone is rotated. Such effects occur when light is reflected off the silk (the structurally oriented rutile needle. inclusions) in a certain way. This is one example where inclusions increase the value of a gemstone. Rubies can furthermore show color changes — though this occurs very rarely — and chatoyancy.

Natural Occurrence

Rubies are mined in Myanmar (Burma), Thailand, Sri Lanka, Tanzania, Kenya, Madagascar, and Cambodia. They have also been found in the U.S. states of Montana, North Carolina and South Carolina. The Mogok Valley in Upper Myanmar has produced some of the finest rubies, but in recent years very few good rubies have been found there. The unique color in Myanmar (Burmese) rubies is described as "pigeon’s blood". They are known in the trade as “Mogok” rubies. In central Myanmar the area of Mong Hsu also produces rubies. The latest ruby deposit to be found in Myanmar is situated in Nam Ya. In 2002 rubies were found in the Waseges River area of Kenya. Sometimes spinels are found along with rubies in the same rocks and are mistaken for rubies. However, fine red spinels may approach the average ruby in value.^[1]

The value of natural rubies varies depending on their size, cut, origin, clarity and quality. As of 2000, a gem quality, uncut one carat (0.2 g) ruby cost about $4,200 USD.^[2] Since it is easy to spot synthetic rubies by their lack of natural inclusions, they have not greatly affected the price of natural rubies.^[3]

Treatments and enhancements

Improving the quality of gemstones by treating them is common practice. Some treatments are used in almost all cases and are therefore considered acceptable. During the late 1990s, a large supply of low-cost materials caused a sudden surge in supply of heat-treated rubies, leading to a downward pressure on ruby prices.

Improvements used include color alteration, improving transparency by dissolving rutile inclusions, healing of fractures (cracks) or even completely filling them.

The most common treatment is the application of heat. Most if not all rubies at the lower end of the market are heat treated on the rough stones to improve color, remove purple tinge, blue patches and silk. These heat treatments typically occur around temperatures of 1800°C (3300°F).^[4] Some rubies undergo a process of low tube heat, when the stone is heated over charcoal of a temperature of about 1300°C (2400°F) for 20 to 30 minutes. The silk is only partially broken as the color is improved.

A less acceptable treatment, which has gained notoriety in recent years, is lead glass filling. Filling the fractures inside the ruby with lead glass dramatically improves the transparency of the stone, making previously unsuitable rubies fit for applications in jewelry. The process is done in four steps:

If a color needs to be added, the glass powder can be "enhanced" with copper or other metal oxides as well as elements such as sodium, calcium, potassium etc.

The second heating process can be repeated three to four times, even applying different mixtures.^[5] When jewelry containing rubies is heated (for repairs) it should not be coated with boracic acid or any other substance, as this can etch the surface; it does not have to be "protected" like a diamond.

Synthetic and imitation rubies

In 1837 Gaudin made the first synthetic rubies by fusing aluminium at a high temperature with a little chromium as a pigment. In 1847 Edelman made white sapphire by fusing alumina in boric acid. In 1877 Frenic and Freil made crystal corundum from which small stones could be cut. Frimy and Auguste Verneuil manufactured artificial ruby by fusing BaF₂ and Al₂O₃ with a little Chromium at red heat. In 1903 Verneuil announced he could produce synthetic rubies on a commercial scale using this flame fusion process. ^[6]

Other processes in which synthetic rubies can be produced are through the Pulling process, flux process, and the hydrothermal process. Most synthetic rubies originate from flame fusion, due to the low costs involved. Synthetic rubies may have no imperfections visible to the naked eye but magnification may reveal curves striae and gas bubbles. The fewer the number and the less obvious the imperfections, the more valuable the ruby is; unless there are no imperfections (i.e., a "perfect" ruby), in which case it will be suspected of being artificial. Dopants are added to some manufactured rubies so they can be identified as synthetic, but most need gemmological testing to determine their origin.

Synthetic rubies have technological uses as well as gemological ones. Rods of synthetic ruby are used to make ruby lasers and masers.

Imitation rubies are also marketed. Red spinel, red garnet and glass have been falsely named as rubies. Imitations go back to Roman times and already in the 17th century techniques were developed to color foil red -- by burning scarlet wool in the bottom part of the furnace -- which was then placed under the imitation stone. ^[7] Trade terms such as balas ruby for red spinel and rubellite for red tourmaline can mislead unsuspecting buyers. Such terms are therefore discouraged from use by many gemological associations such as the Laboratory Manual Harmonisation Committee (LMHC).

Records

The Smithsonian's National Museum of Natural History in Washington DC, has received one of the world's largest and finest ruby gemstones. The 23.1-carat Burmese ruby, set in a platinum ring with diamonds, was donated by businessman and philanthropist Peter Buck in memory of his wife Carmen Lúcia. This gemstone displays a richly saturated red color combined with an exceptional transparency. The finely proportioned cut provides vivid red reflections. The stone was mined from the famous Mogok region of Burma (now Myanmar) in the 1930s.^[8]

Historical and cultural references

Valley of rubies

Of the world's rubies, 90% currently derive from Myanmar (Burma) whose red stones are prized for their purity and hue. Thailand buys the majority of Myanmar's gems. Myanmar's "Valley of Rubies", the mountainous Mogok area, 200 km (125 miles) north of Mandalay, is noted for its rare pigeon's blood rubies and blue sapphires. But working conditions in the mines are horrendous. Debbie Stothard of the Alternative ASEAN Network on Burma stated that mining operators used drugs on employees to improve productivity, with needles shared, raising the risk of HIV infection: "These rubies are red with the blood of young people." Brian Leber (41-year-old jeweler who founded The Jewellers' Burma Relief Project) stated that: "For the time being, Burmese gems should not be something to be proud of. They should be an object of revulsion. It's the only country where one obtains really top quality rubies, but I stopped dealing in them. I don't want to be part of a nation's misery. If someone asks for a ruby now I show them a nice pink sapphire."^[11] In 2007, following the crackdown on pro-democracy protests in Myanmar, human rights organizations, gem dealers, and US First Lady Laura Bush called for a boycott of a Myanmar gem auction held twice yearly, arguing that the sale of the stones profits the dictatorial regime in that country. ^[12]

Contents