To use all functions of this page, please activate cookies in your browser.
With an accout for my.chemeurope.com you can always see everything at a glance – and you can configure your own website and individual newsletter.
- My watch list
- My saved searches
- My saved topics
- My newsletter
Ruby is a pink to blood red gemstone, a variety of the mineral corundum (aluminium oxide). The common red color is caused mainly by the element chromium. Its name comes from ruber, Latin for red. Other varieties of gem-quality corundum are called sapphires. It is considered one of the four precious stones, together with the sapphire, the emerald and the diamond. Improvements used include color alteration, improving transparency by dissolving rutile inclusions, healing of fractures (cracks) or even completely filling them.
Prices of rubies are primarily determined by color (the brightest and best "red" called Pigeon Blood Red, command 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.
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 (of which heat treatment is the most common practice), and rubies which are completely untreated and 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.
Treatments and enhancements
Improving the quality of gemstones by treating them is common yet time-consuming practice. Some treatments are used in almost all cases and are therefore considered "acceptable" practices. The most common treatment is using heat. Most if not all rubies at the lower end of the market are heat treated. Heat treatment is performed on the rough stones to improve color, remove purple tingle, blue patches and silk. These heat treatments typically occur around temperatures of 1800°C (3300°F). 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, and one which has gained notoriety in recent years is "Lead Glass Filling" of Rubies. By filling the fractures inside the ruby with lead glass the transparency of the stone is dramatically improved making previously unsuited rubies now fit for applications in jewelry. The process is typically done in 4 steps:
In case 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 consecutively, even applying different mixtures.
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. 
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.
Imitation rubies have also been present in the gemstone market for some time. Red spinel, red garnet and even 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.  Trade terms such as balas ruby for red spinel and rubellite for red tourmaline can mislead unsuspecting buyers. Such terms are therefore discouraged from being used by many gemological associations such as the Gemological Institute of America (GIA).
Although pieces of red corundum can be found weighing many kilograms, they are generally not of sufficient quality to be valuable as gemstones. For this reason, auction prices are the best indicator of a stone's true value, and prices do not necessarily correlate with size. As of 2006, the record price paid at auction for a single stone was $5,860,000 for an unnamed 38.12 carat cabochon-cut ruby.
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."  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 thrice yearly, arguing that the sale of the stones profits the dictatorial regime in that country. 
|This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Ruby". A list of authors is available in Wikipedia.|