Sapphire, possibly the most popular precious stone in Europe and North America comes, with the exception of ‘ruby-red’, in all shades of the rainbow. The varying colours are caused mostly by different trace elements. However this variety of the mineral corundum has been admired for millenia primarily for its elusive blue hue. The colour of the heavens, blue calms the eye and stands for timeless elegance.
The best blue sapphires trend between two colour ideals according to personal and cultural taste – a medium cornflower blue at the lighter end and a medium dark royal blue at the darker end. Both colour tones ideally contain approximately 85 to 90% blue with a minor 10 to 15% secondary purplish to violet adding warmth and richness to the blue. The colouring agent in blue sapphire is titanium oxide.
Since sapphire is a dichroic gem, it will display two distinct colours according to its orientation, one parallel to the primary crystal axis and the other exactly perpendicular to it. Usually the ‘c-axis’ will display a violetish blue hue and 90 degrees to it a distinct greenish blue. However no green should be visible face-up as it will always lower the value of a blue sapphire.
Although a good crystal adds greatly to beauty and value and separates the best sapphires from the rest, top stones also contain a veil of very fine rutile (titanium oxide needles) ‘silk’ giving them a velvety appearance. This silk softens yet adds vibrancy to the colour by refracting light internally throughout the stone. Prime examples are the legendary Kashmir Sapphires which are noted for their neon to dark cornflower blue colour and slightly sleepy look. Since they also lack chromium Kashmir sapphires hardly ever shift colour in different lighting environments. Stones of similar appearance have also been found Andranodambo, Madagascar and Elahera, Sri Lanka. Second by pedigree are Burmese sapphires, which ideally face up a touch darker and feature a more electric blue colour and an excellent crystal. Both sources have their devoted followers. Next, come classic blue sapphires from Sri Lanka, the island of gems, which tend to contain a touch more purplish in the blue and coarser silk but otherwise may resemble both aforementioned origins closely and can be just as beautiful. Despite the best sapphires from Madagascar easily outrivaling Sri Lankan stones, the majority of material from the various mining localities across the island features even coarser zoning and an often poorer, murkier crystal. Other sources of lesser importance include Kanchanaburi, Thailand which produces the odd stunning iron-rich yet pure deep blue stones as well as Nigeria, Tanzania (Umba and Tunduru) and Australia. The latter origin is particularly notorious for its ‘inky’ oversaturated sapphires.
In order to lighten or darken the colour, or improve transparency by dissolving excess ‘silk’, sapphires have since antiquity been subjected to heat treatment. Unfortunately higher temperatures reached by modern-day methods in particular often slightly reduce transparency. Whilst historically accepted by the trade, only the finest quality heated stones nowadays find a ready market. The price of such goods is typically around a fifth to a quarter that of unheated stones of equivalent quality from non-pedigree sources.
Since colour zoning is also common in sapphires cutting needs to accommodate this. Hence minor symmetry faults such as lopsidedness and slightly off-centre culets are, within reason, tolerated. The emerald cut is the preferred shape in sapphire followed by cushion and oval.
The second most popular sapphire colour is pink. The finest pink stones come from Mogok, Myanmar. These are basically unsaturated rubies and can be a very hot ‘bubblegum’ pink. Others may flash a vibrant ‘Fuchsia’. Prices for the very best specimens can surpass those of fine blue Burmese sapphires. Another source of vivid pink sapphire is Luc Yen in Vietnam.
The two other sources of fine soft pink sapphires are Sri Lanka and Madagascar. Stones from these two sources either tend towards magenta, the second most valuable colour after straight pink or show a secondary purplish hue.
Purple sapphires occur in fuchsia, mauve, lilac and violet shades. Generally rare bright lilac to amethyst shades is the most appreciated. Many purple sapphires are colour changers shifting colour from artificial to natural sunlight due to traces of the element Vanadium.
The most significant producer of extremely fine purple and colour changing sapphires is Burma. However, it is surpassed, at least in quantity by both Sri Lanka and Madagascar.
An extremely rare as well as beautiful rich plum to aubergine variety has been occasionally found in Burma.
Today a superb Padparadscha Sapphire is the most valuable variety after Kashmir sapphire. This is largely due to Asian demand.
The name is derived from Sinhalese and refers to the colour of the budding lotus flower which is a striking reddish orangy Pink. Only Stones from Sri Lanka, its classic source, will also be certified as Padparadscha by all the reputed labs.
The precise hues falling under this colour term range from a pinkish to pink-orange and orangy to orange-pink. Additionally, a minor purplish touch adding depth is permissible and a little red even preferred. Since Padparadschas are rarely dark toned, highly saturated stones are exceedingly rare. Visually similar stones are sometimes found in Madagascar and rarely Vietnam.
Another source of distinct pinkish to pink (reddish) Orange sapphires is Tanzania. East African stones often exhibit a richer, though less vibrant and less delicate orange colour. They are sometimes spoilt by undesirable brown and may feature poorer crystal quality.
The last noteworthy sapphire colour is yellow. Revered for its astrological significance it remains highly popular on the Indian subcontinent. In the west, demand exists primarily for unheated clean and well saturated yellow stones. The best examples come from Burma and may show a touch of orange. The most important producer in terms of volume, however, remains Sri Lanka.
Lastly, fine quality Star Sapphires have their devoted followers. They remain largely collector’s stones and are mainly in demand in Asia or for use as centre stones in gentlemen’s rings.