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Ruby – Our guide to the fiery July birthstone

Ruby is widely recognised as the July birthstone. It has been revered for millennia by many different cultures, including the Mogul dynasties of ancient India who referred to it as the “king of gemstones.” Akin to sapphire, ruby is a member of corundum family. Its red colouration is caused by traces of chromium in its structure and it is, in essence, a red ‘sapphire’ (sapphire being the full remaining colour spectrum). The more chromium found in a ruby, the richer its red appearance and the greater its florescence, which has the effect of further deepening the colour. Florescence is most clearly visible in ultraviolet (UV) light so rubies give off their most dazzling colours in natural sunlight. Rubies with the highest concentrations of chromium (and hence the deepest colouration) tend to be found in marble so these are the most highly desired examples. Basalt formed specimens are created when molten lava cools and solidifies and they tend to have a higher iron content, making them darker in appearance and reducing their florescence. Ruby is also found in an amphibole-bearing gneiss (a rough-grained metamorphic stone), resulting in stones of desirable colour which can be said to be between marble and basalt origin examples in terms of overall qualities. Scientifically synthetic ruby was actually used to create the world’s first laser in the early 1960s. For jewellers and jewellery lovers it is the stone’s fiery colour and durability, at 9 on the (1-10) Moh’s hardness scale, placing it just behind diamond at 10, that makes it so appealing.

(A “pigeon’s blood” Mogok ruby set into a ring with diamonds)

Due to its colour, ruby has often been likened with blood and some ancient cultures actually believed that it stopped haemorrhaging, cured inflammations and calmed the bad tempered. It is no surprise that the finest rubies are referred to as “pigeon’s blood” specimens. Burma (Myanmar) is home to some of the finest examples of pigeon blood rubies and the ancient warriors from this land revered the stone and thought it brought them luck on the battlefield. Other cultures believed that ownership of a ruby brought prosperity, wealth, happiness and love. The Mogok region of Burma is famous for the quality of the rubies it produces, as these display the finest red fluorescence and light scattering inclusions. Vietnam has begun to develop its ruby mining industry, where the stones are predominantly to be found in the high quality marble beds. The Luc Yen region of the country in particular is the origin of some of the finest purplish-red rubies, in a an area were artisanal miners labour to unearth life-changing stones amid the heat and humidity of the paddy fields and jungle clad mountains. In recent years Mozambique has risen to prominence in the ruby industry, as Gemfields (the De Beers of the coloured gemstone market) have developed sites such as Montepuez. Many of these stones are of fine quality but they are usually trumped by the top echelon Mogok specimens. Basalt bedded rubies have been found in quantity along the Thai-Cambodian border and many others have been discovered in Sri Lanka, Madagascar and Tanzania.

(At $3 million in 1989, the Harry Winston ruby slippers are the most expensive shoes in the world!)

As well as being the July birthstone, ruby is also associated with fifteenth and, more commonly, fortieth anniversaries. One of the most extravagant uses of rubies were the Harry Winston Ruby Slippers, commissioned to mark the fiftieth anniversary of the film “The Wizard of Oz” in 1989. The slippers contained over 4,600 rubies, totalling over 1,350 carats, and over 50 carats of diamonds, at a cost of more than $3 million in 1989 (over $6 million in 2018 prices). As with many coloured gemstones, colour is the most important factor in determining the value of a ruby. The most desirable colour can best be described as a vibrant red to slightly purplish-red, without too much purple or orange. The colour saturation must also be just right, as there is a ‘sweet’ spot that is not too light nor too dark. Expect to find inclusions when looking at a ruby, as examples that are totally inclusion free are likely to be synthetic substitutes. However the amount of inclusions, their location and their impact on transparency and brightness does significantly affect the value of a stone. The crystalline structure of a ruby determines the stone’s suitability for different cuts. Most ruby crystals exhibit a flat tabular hexagonal geometry but less commonly some examples may contain elongated crystals. Although rubies are found in a wide spectrum of carat sizes, very fine examples over a carat are rare (and hence expensive) and price per carat increases exponentially as you pass key numerical milestones (such as 1.0, 1.5, 2.0 etc).

(A map showing the principal locations of gemstone production)

When it comes to caring for rubies, it is advisable to stick to warm, soapy water and a soft cotton cloth. Ultrasonic and steam cleaning devises are generally safe for untreated stones, heat treated and lattice diffused rubies. However, this should only be done by an experienced professional and fracture or cavity filled and dyed stones should only be cleaned with soap and water. Over 90% of rubies are treated in some way, often with heat to improve their red colouration and/or eliminate “silk” (very small needle-like inclusions) which can have an adverse effect on the stones appearance. This has an effect on the stone’s value so it is important to check the certificate carefully and only purchase stones that have been certified by a leading gem lab. Properly disclosed treatments are fine as long as they are honestly declared and result in a stable outcome for the stone itself. As with emeralds, fracture filling of surface reaching fissures is a common practice and this should only be done with natural oils, as glass filled rubies can literally disintegrate if they are knocked! Stones that have been dyed should also be avoided because their colour can deteriorate over time and they respond poorly to changes in humidity, temperature and air pressure. Key to any stone purchase is its gemmological report, which demonstrates in black and white whether a stone is natural or synthetic, treated or untreated (and if treated, the exact type of treatment that has been applied).

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