Ruby - King of Gemstones
Ruby is the red variety of the gem species corundum, all other (some may say, inferior) colours of corundum are termed sapphires. Generally, the term sapphire when used alone refers to the blue variety. The array of other colour variations, such as pink, yellow, Padparadascha or green are also referred to as sapphires, but their hue is stated beforehand.
Mineral Species: Corundum
Refractive index: 1.76 – 1.77
Specific gravity: 3.9 – 4.1
Colour range: Orangish red to purplish red
Chemical composition: Al2O3
Crystal Structure: Trigonal
Typical cutting style: Oval and cushion mixed cut
Called ‘ratnaraj’ in Sanskrit meaning ‘king of precious stones’, ruby is one of the most historically important coloured stones, and has thus played a part in human culture for thousands of years. For instance ruby has been mentioned by Pliny in the first century AD, as well as being mentioned 4 times in the bible (but then again so were talking bushes). Anyhow…. clearly, these are stones of importance and have been for centuries!
No gemstone worth its weight in – well its weight in gemstone, would be complete without a comprehensive set of worldly legends surrounding it……. In India, it was believed that rubies enabled peace between enemies, in Burma rubies were said to make warriors invincible in battle (If they inserted them under their skin!); and in the modern day west, it is still believed by some that rubies guarantee health, wealth, wisdom, and success in love. Less historically significant, but still highly relevant if you’re in sales, marketing gods somewhere in the West, designated ruby as the official birth stone for July as well affirming it is the only way to appropriately celebrate a 40th wedding anniversary.
Until the invention of modern gemological testing methods, it was thought that all red stones were ruby. One of the most famous “rubies”, the Black Prince’s Ruby in the British crown jewels, is in fact a very beautiful red spinel.
These little red sparkles are surprisingly pricey – in some cases even more so than diamonds!
In small sizes the price of good quality diamonds far exceeds that of ruby, for example one popular jewellery wholesale supply company sells a single 2mm VS / GHI diamond for $28.35 whilst a 2mm ruby of excellent quality is sold for only $9 – bargain!
However large fine quality rubies are much rarer than large fine colourless diamonds and are thus priced accordingly. For example, let’s take a look at The Sunrise Ruby pictured at the top of this article. This bad boy is a 25.59-carat Mogok Burmese Ruby set in a fabulous ring designed by Cartier, supported by a couple of insignificant side diamonds. This beauty – the real King of Gemstones, sold at Sotheby’s Geneva, May 2015 auction for $30,335,968 ($1,185,451 per carat).
For comparison purposes alone, and not because I personally want to argue the superiority of coloured stones we can now consider diamonds. The highest price ever paid for a single colorless diamond at auction was for a 118.28ct D flawless gem sold Sotheby’s Hong Kong, October 7, 2013. The diamond sold for a total of $30,680,000 (a paltry $259,000 per carat).
By far, the most expensive coloured gemstone, ruby can beat all records…… except that of coloured diamonds – but these guys are in a league of their own! On 4 April 2017 in Hong Kong, Sotheby’s set a new world auction record for any diamond or jewel when the Pink Star, a 59.60-carat oval mixed-cut Fancy Vivid Pink Internally Flawless diamond, sold for $71.2 million
As with most coloured stones, the primary consideration when buying a ruby is its colour. The purer the red, the more valuable the stone. Any modifying colours generally detract from the value of a pure red hue. Orangey red stones are predominantly considered less valuable than slightly purplish red stones. However, beauty is in the eye of the beholder, and it would likely not be the best move to inform ones customer that they have cheap taste.
To be of ideal colour, it must be neither too dark nor too light. If the tone (degree of lightness or darkness) is too dark, it has a negative effect on the stone’s brightness. If the tone is too light, the stone is considered pink sapphire. Gem dealers worldwide however tend to debate the borderline between pink sapphire and ruby. Historically the term ruby referred to all shades of red (including pink), and in Asia where many rubies and sapphires are mined, stones that would be classified and called pink sapphire in the west, are here classified as ruby.
The finest rubies also display a particular phenomenon – which gives their colour an extra POW! According to the ancient Hindus, “Ruby’s light could not be extinguished nor hidden by clothing….” With science now on our side, the magical light of ruby can now be explained: ultraviolet light causes the chromium in rubies to fluoresce and the UV in sunlight is enough to cause some rubies to actually glow. Not magic, but still awesome.
Rubies are generally expected to contain inclusions, however inclusions that detract from a gemstone's attractiveness or cause durability issues (such as large fractures) significantly lower the value of the stone. Some inclusions however, are considered beneficial to the value of ruby. For example many rubies contain microscopic inclusions of rutile, which can scatter the light and give the ruby a desirable soft red colour. If enough inclusions are present, they can give rise to a an effect called ‘asterism’ and create a star effect in the ruby.
Sold in Christies Hong Kong Magnificent Jewels auction on 27 November 2012, for 1,247,412, this certified Myanmar unheated 19.53ct ruby surrounded by diamonds by ETCETERA, is an example of the finest star rubies. Photo credit: Christies
Most rubies are cut to retain maximum weight. Therefore some deviations from a perfect cut are expected as long as they do not detract from the overall appearance of the stone. Most rubies are cut as an oval or cushion mixed cut with a step cut pavilion and brilliant cut crown.
Commercial-quality rubies are commonly available in a wide range of sizes, however fine quality rubies are rare in sizes over 1ct – much rarer than diamonds. The price per carat goes up significantly for ruby as it increases in size.
By far, the finest and most expensive rubies sold today and historically are from the Mogok region of Myanmar. Rubies from this area are held in such high regard, that to have a fine stone certified by a gemmological laboratory as having a Mogok / Burmese pedigree will put a premium on the price. Sri Lanka is thought to be one of the earliest sources of ruby, with some sources suggesting rubies were mined their as early as 2000 years ago. Other significant sources of rubies include:
Rubies have been subject to treatment for centuries, and most rubies on the market nowadays are assumed to have undergone some form of heat treatment unless stated otherwise. Detection of basic heat treatment can be very difficult, especially in gemstones lacking in inclusions (the inclusions can often give indications to treatments). Even gemmological laboratories will not go so far as to say – “this stone has not been heat treated”, but instead will say “no indication of heat treatment”.
Heat treatment is not overly controversial and it is assumed unless stated otherwise. Treatments that can cause issues however are fracture filling and lattice diffusion – not because they are bad in themselves, they allow beautiful gemstones to be marketed at a lower price. However, some unscrupulous sellers will market the stones as natural and not disclose their treatment status to buyers – A**holes. Stones treated in either of these ways are sold at a considerable discount to their natural counterparts and so disclosure from the seller is very important. As a buyer it is wise to consider the old saying “if it sounds too good to be true, it probably is”.
Lead glass filling / fracture filling / flux healing
Originally rubies could be filled in a way similar to which diamonds or emeralds are filled, either with oil, resin or glass, which then reduces the appearance of cracks within the gemstones. In this case the treatment is neither permanent nor stable.
In a relatively new treatment, rubies (mostly from the Mong Hsu region of Myanmar) are treated with a flux material to improve their clarity and brighten the colour. Two processes occur simultaneously which help improve the clarity of the gemstone. First, the flux dissolves the surface of the fractures and partially re-heals them with what is basically synthetic ruby. Then often the remainder of the crack is simply left filled with a high lead glass residue. The high lead glass residue has a slightly different lustre to that of the ruby and so when the surface is examined under reflected light, differences can be seen and flux filling detected. Whilst the re-healed fractures are stable – the left-over flux filling is not durable and if flux filled rubies are heated, polished or cleaned with solvents, damage can occur.
Beryllium treatment / diffusion treatment / new heat treatment
Most rubies that are treated in this way are distinctly orangish. Often referred to as Songea Sapphire (to distinguish them from rubies, and avoid freaking customers out), the stones are heated to a very high temperature in the presence of colour causing chemicals such as beryllium. The chemicals then penetrate into the crystal structure of the gemstone and alter its colour. The colour can go all the way through a gemstone or just affect a shallow area close to the surface. The colour is stable unless the stones are recut – when the coloured surface may be removed. Inherently there is nothing wrong with this treatment, it is stable and the stones require no special care once set in jewellery, the only problem with this is disclosure about the treatment. Gemstones are valuable to a significant extent because of their rarity (and in the case of diamonds – marketing). Although these stones may look the same as their naturally coloured counterparts, they lack their rarity and therefore should be priced accordingly. Distinguishing features of high temperature heat treatment with chemicals are blue disk like inclusions, as well as surface-related colour zoning, however often neither are present.
A synthetic gemstone is a gem that has the same chemical composition and crystal structure as its natural counterpart, however it was produced in a laboratory. Rubies have been synthesized for over 100 years. Initially these synthetics were easy to differentiate from their natural counterparts through simple magnification, but as techniques have improved, it has become more difficult to make the distinction. Most synthetic corundum is still made utilising the flame fusion (verneuil) method that was initially discovered in 1902 by the French chemist Auguste Verneuil. These gemstones show curved growth lines due to the way in which the crystals are made. Curved growth of this nature is never seen in natural corundum.
Care and Consideration for Jewellers
In natural gemstones, ruby’s hardness is second only to that of diamond. With a hardness of 9 on the Mohs scale, it is difficult to scratch and therefore a feasible option for an engagement ring. However, care must still be taken when using abrasive papers – these are generally made using a corundum grit and therefore can still scratch all coloured gemstones including ruby and sapphire (varieties of corundum). Generally, sandpapers should only be used with diamond and no other coloured stones. The same is true for most rubber wheels as they are usually impregnated with some form of corundum abrasive – pumice wheels are the exception here.
For rubies and sapphires that haven’t undergone treatments such as fracture filling, and do not contain cracks, no special care is needed. It is fine to put them in the ultrasonic, steam clean them, and plate metal with them in place. With a hardness of 9 and toughness rated as good, they should pose no major issues when setting, unless of course fractures are present.
Rubies….. beautiful, durable and admired by royalty (and me). As long as deposits keep up with demand, I don’t foresee this darling of the gem world losing its title of “King of Gemstones” any time soon.
References and Further reading:
Hughes. R, 2014, Ruby and Sapphire a Collectors Guide, Thailand, Gem and Jewellery Institute of Thailand