June 24, 2021
In the image: ruby deposits map
Sometimes, geographic origin (a deposit) also influences the cost of natural precious stones. Myanmar (Burma) is a source where top quality rubies are mined. Burmese ruby is a well-establish brand in the world of gems and jewellery. Unheated «Peigeon’s blood» rubies from Burma (Mogok valley and Mong Hsu) are the most valued. Significant share of the world market belongs to red corundum of African origin, in particular coming from Mozambique. Among Mozambican rubies there are samples as beautiful as Burmese rubies. Also mining is provided in Thailand, Madagascar, Tajikistan, Tanzania, Vietnam and other countries. Indian rubies comes in larger size they tends to have poor transparency. By the way, rubies brought from Thailand in most cases were not mined in Thailand. There is just the main center of cutting rubies.
In the left photo: samples from Mozambique, 4.07 and 4.02 cts (heated) and 3.02 ct (unheated)
Quality of cut and attractiveness of a form often influence an appearance of stones and their cost. Symmetry, correct proportions, lack of scratches, chips and mechanical damage are very important. Often, Asian cutters try to save more mass in a finished stone, for this they make deep pavilions (lower part of a stone). Some rubies with deep pavilions may in form resemble acorns, the “face” of a stone becomes disproportionately small, because in a lower part is concentrated a significant part of the volume of a stone. The opposite case is when a cut of a stone has wrong proportions, and the lower part of the stone, in contrast, has a lack of depth. At the same time, a “window” is formed in a stone – a light area in the center of a stone, which does not return light to an eye of an observer. Such stones should be cheaper than rubies with the correct proportions.
“Practical advice. Judge attractiveness of form and quality of cutting at whole. Pay attention of a symmetry of a gemstone, whether is a lack of color in a center of a stone, a window, does it affect beauty? Is a pavilion too deep? Look at a quality of polishing, are there any scratches, chips on surfaces of facets and edges? Many surface defects can be easily removed with inexpensive re-cutting or polishing.“
In the photo: rare top quality unheated ruby weighed 4.03 ct, Burma
For rubies is typical to be improved with different methods of treatment. Treatment is aimed on color improvement, also it is possible in some cases to improve clarity. The most wide-spread method is heat treatment. They are heated in special furnaces to temperatures in range of 800-1900 degrees. As a result of heating, the color of natural samples can become more saturated, it is also possible to lighten a little too dark stones or remove unwanted shades (for example, purple), reducing a cost. Clarity improvement of these stones as a result of heating is due to the fact that thin needle inclusions of rutile, which often form noticeable whitish clusters, can melt. Heat treatment is applied to about 90% of all mined rubies. The cost of a heated samples can be about 2-3 times higher than unheated stones of the same quality. This is due to the fact that unheated rubies with a good color by nature are much more rare stones and valued.
The cheapest rubies that were improved are heat treated samples with lead glass filling cracks. This method hides cracks in rubies, significantly improves the transparency and due to this color also becomes bright. Glass can occupy even 50% of the stone volume. Cost of such ruby-glass composites can be just $ 1-20 per 1 carat. Heat treatment and glass filling are the most common types of ruby enhancement. Less common practice is heat treatment in presence of flux, then some cracks can be “sintered” and become less noticeable. As factor of enhancement strongly affects prices, in addition to words of a supplier, it is desirable that natural origin is confirmed by a certificate from a well-known independent gemological laboratory.
Natural rubies has gemological varieties. For example, gemstones with optical effects. Star rubies display the phenomenon of asterism, and on surface you can see a 6-ray star, which slides on a surface of a cabochon. Another effect of rubies – the effect of cat’s eye, when a white light strip moves through surface of a cabochon. Both these phenomenons are associated with presence of oriented needles of rutile. Such samples are always unheated, otherwise rutile needles would dissolve from heating. Among the rubies there is a rare variety – “Trapiche”, which is highly valued by collectors, but rarely presented in jewelry. Their feature is that they have in the cross sections of crystals 6 sectors, separated by white rays. Crystals of rubies “Trapiche” usually come from Burma (Myanmar).
In the right photo: the star ruby cabochon from Vietnam weighed 27.69 ct
Rubies in addition to natural origin may also have a synthetic origin. They are grown by various methods. They can have a good color and excellent clarity, but their value is usually very small, because in comparison with natural gemstones, synthetic rubies are not rare. For confirmation of a natural origin, and also diagnostics of treatment, definition of the field (especially for samples from Burma) and color (“pigeon’s Blood” or not) it makes sense to request from sellers for expensive rubies certificate from independent Gemological laboratories. Keep in mind that opinions of different laboratories on the same sample regarding the determination of the fact of treatment or attributing color of a stone to the commercial top color “pigeon’s Blood” may sometimes not coincide with each other. Therefore, very expensive auction level rubies can be often accompanied with certificates from several laboratories. Some of the most reputable laboratories are: GIA, Gubelin Gem Lab, SSEF and AGL. In the Asian market of rubies are also very popular certificates from the famous Swiss laboratory GRS.
In the left photo: a fragment of GRS certificate on the Burmese ruby
“Practical advice. Ask a seller about the presence of a certificate for the stone. What is its geographic origin? Was it enhanced? If so, in what way? A certificate will help to answer these questions. Find out information from a seller.”
– In the first part of the article we tell about a color of ruby, clarity and weight.
– In the third part of the article we show you real prices on rubies
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