Rubies, along with diamonds, emeralds and sapphires, are a precious gem in high demand. They are hard gemstones (although not as hard as diamonds), a quality that makes them fairly scratch resistant and practical to wear routinely, rather than just on special occasions. Rubies, along with their sister sapphires, are formed from the mineral corundum. The deep red saturation of the finest rubies has long been their biggest market asset and they have the unique quality of being able to attract very high prices even with significant inclusions and in some very rare stones this can lead to the "star stone" effect. The growth of synthetic diamonds (see our previous article - "Synthetic diamonds - the industry's greatest challenge") has been mirrored by a sharp rise in the number of lab grown rubies. It is also worth noting that the vast majority of rubies have undergone some form of treatment or enhancement so it is well worth understanding the effects these can have on value and to also look for stones that have been certified by a well respected laboratory.
(An example of a deep red 'Pigeon's blood' ruby)
Colour
With rubies (when considering the 4 C's) it is the clarity and the carat that are of significantly less importance and the colour and carat size the main determiners of price. The coveted "pigeon blood red" variety from Myanmar (Burma) are by far the most sort after (especially in the USA, due to a trade embargo imposed in 2003). Although some price guides do exist, such as Gemval.com and the International Gemmological Society (IGS), there is no definitive equivalent to the Rapaport Price with colourless diamonds. The GIA colour grading system (applied to all gemstones) recognises three characteristics: hue; tone and saturation. The standard hues are red, pink orange, yellow, green, blue, violet and purple. Tone defines the relative lightness from zero (colourless) to 10 (black). Finally saturation relates to the intensity of colour, from one (grayish or brownish) to 6 (vivid). The dominant hue is in upper case and other hues present are in lower case and can be further defined as "sl" (slightly) or "st" (strongly). The colour of the finest rubies are referred to as "R 6/6," where "R" pertains to the dominant hue of red, the first 6 to a deep tone and the second 6 to the most vivid possible saturation.
(Examples of rubies of different hue, tone and saturation)
Clarity
Clarity relates to the transparency of a stone and any intervening objects, such as inclusions, that may influence how light is transmitted and refracted through the crystalline structure of the stone. All corundum stones, including rubies and sapphires, are referred to as being of Type II clarity. That is to say they usually contain inclusions within their structure. These can exist inside the stone as a solid liquid or a gas and they can also include crystal needles of the mineral rutile, which can create a highly desirable 'star' effect. The highest value stones are referred to as "loupe clean," or VVS (Very, Very Slightly included), that is to say the inclusions themselves are not visible to the eye under 10 times magnification. Loupe clean, stones are extremely rare, especially those above 1 carat. Following on down the scale from these are "eye clean," or VS (Very Small inclusion) stones with no inclusions visible to the naked human eye. SI (Small Inclusions) and I (Included) may contain inclusions that are visible to the naked eye. Naturally value diminishes from VVS - VS - SI - I and the more inclusions the less durable the stone may be.
(An inclusion deep within the crystalline structure of a ruby, seen under 40 X magnifcation)
Cut
Most rubies are "native cut," that is to say they are cut and polished in or near their place of origin. Despite the fact that the cut has the least effect on price of the 4 C's when it come to rubies, those cuts that maximise light refraction and reflection or enhance the colour of the stone, such as step cuts, can impact the finished stone's final value. Emerald cuts add the most value to a ruby, followed by round, pear and marquis shapes. Oval and cushion are the most common cuts for these stones. Cabochon cuts can produce the much venerated "star stone" effect, if the rutile crystal inclusions are found within the stone in a conducive position. Cabochons also carry the unique advantage of being ideal for rubies that contain inclusions that would be far too prominent for faceting. Due to the fact that most rubies are native cut, the skills require to cut and polish these precious gemstones are highly sought after in the Western world and consequently stones cut far away from the country of origin can often be extremely expensive.
(Some of the more common ruby cuts)
Carat
Size is critical with rubies and those stones over 1 carat are extremely rare. As with most precious gems the price per carat of a fine ruby increases exponentially following a bell-curve which 'jumps' further still when a stone crosses key carats. However some colossal rubies have been produced, including the 25.59 carat Burmese 'Sunrise' ruby, which fetched over $30 million at auction in 2015.
(No exact distinction exists between a pink sapphire and a ruby)
7 top buying tips
- Red and purplish red are the colours that fetch the highest price but consider subtle variations on these to significantly lower the cost without a noticeable impact upon the visual result.
- It is also worth considering that small eye visible inclusions (those visible with the naked eye at 6 inches) can sometimes give the stone an aesthetic quality in its own right, far from necessarily being an undesirable factor. The setting of the stone can also have a profound effect on the visibility of inclusions as well as the depth of the colour.
- Synthetic rubies have the same chemical composition as natural rubies and they have been available since the nineteenth century. It is very hard for even a trained gemmologist to distinguish these from natural stones so certification is crucial!
- Unlike synthetic rubies, simulated rubies are not rubies at all, they are simply less expensive stones (such as garnet or spinel), glass or plastic adapted to appear to be rubies although they may sometimes be combined with small quantities of very low quality natural ruby.
- Natural rubies can be found in every continent on earth but national colour associations have built up with, for example, "Burmese" red and "Thai" red rubies gaining notoriety. You may also come across the terms "French," "Ceylon" or even "African" rubies but it important that these are simply marketing names and they can sometimes mislead a buyer as to the stone's true origin.
- All red varieties of gem quality corundum stones are regarded as rubies and all other coloured varieties of corundum are referred to as sapphires. However the boundaries between a pink sapphire and a ruby are not well defined or entirely agreed upon. Rubies are rarer than sapphires so this distinction does take on an important financial consideration.
- Heat treatment is a very common practice with rubies and it is used to remove rutile inclusions and to enhance colour tone and saturation. Unlike coloured diamonds, this process is not dissimilar to the natural processes the stones undergo in nature so it does not have a significant effect on price. As with other gemstones, filling fissures or fractures with polymers, resins or leaded glass will adversely affect the value of a stone.
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