Sapphire
Sapphies are more abundant than ruby because its colouring agents (impurities) are more common than those of ruby. The most valuable colour is blue, and Burmese and Kashmir sapphires are the most sought – after gemstones. Kashmir sapphires are mined on the borders of India and Pakistan; the the gems are a deep velvet blue that is sometimes described as cornflower blue. No new materials from Kashmir is appearing on the market as the deposits are virtually worked out. Burmese blue sapphires are an intense, bright blue (royal blue) with a hint of purple.
Sri Lankan blue sapphires have become very popular and range in colour from mid-blue with a tinge of violet to pastel blue. The material regular colour distribution and the Sri Lankan cutters take advantage of this to ensure that some colour is always in the stone's cutlet. This makes a stone appear to have a good colour, even if it is mostly colouress when viewed from the side. Since the 1970s, Sri Lankan geuda - or colourless - sapphire has been heated in a secret process to produce bright, lustrous blue sapphires that are sometimes sold as natural.
Thai blue sapphire, which tends to be rather dark in colour, is produced it huge quantities by the lapidaries who operate in partnership with the Thai miners. Australian sapphires can appear inky in artificial light, so material is sent to Thailand for cutting and heating to lighten and clarify the material. Unfortunately, this can result in the sappties gaining a green tint.
African blue sapphires are variable in colour. Nigerian stones are often very dark, but Tanzania poduces good-quality coloured sapphires, including fine blue crystals. Gem sapphires from Montana are usually pastel violet-blue to steel blue. The colour can be irregular with strong zoning and the material can be included. In general, American sapphires are quite small, rarely over 1 carat, but they are usually natural. However, western mining techniques and labour costs make makes the production of Montana sapphires expensive. Fancy sapphires are found in any colour other than blue. Pink sapphire has become very popular and appears regularly in jewelry designs. The colour can range from soft baby pink to hot bluish pink. Ideally, it should be a uniform, intense pink with no lavender or brown tones. Natural hot pink sapphires have risen in cost significantly and are selling at prices similar to medium-grade blue sapphire. Yellow sapphires are quite common and range from pale yellow to intense amber - they used to be called oriental topaz. Pure golden yellows are quite rare, so many sapphires are heated to a golden colour.
Padparadscha - which is Sinhalese for a type of lotus flower - is a rare and very expensive sapphire that shows pink and orange simultaneously. The source is Sri Lanka. Buyers need to be wary as orange sapphire is frequently offered in place of padparadscha, and pink sapphire is treated with beryllium to create the same effect.
Colourless sapphire is free from any impurities and easy to find in small sizes. Large pieces of colourless sapphire are traditionally heated to blue. Green sapphire used to be called oriental peridot, and often consists of very fine alternating bands of yellow and blue. Unfortunately, the colour can be quite dark and somber. Violet or purple sapphires are coloured by vanadium and occur in pale lilac to deep purple colours. They should resemble fine amethyst, but be slightly redder. Smaller stones are good value, but larger purple sapphires can be expensive.
As with rubies, sapphires have inclusions that denote their origin. For instance, Thai sapphires often contain tiny liquid drops that resemble fingerprints. Rutile needle inclusions in sapphire not only provide "silk" (a silk-like appearance), but also asterism. Ideally, star sapphires should have an intense, translucent blue colour (not grey or black, as is common), with mineral hexagonal banding and well defined and centred stars. Cracks, pits and uneven base are common failings and devalue the stone. There is a practice among Thai and Sri Lankan lapidaries of gluing the base of star sapphires together if a section breaks off during cutting. This might make the stone appear tidy and make it easier to set, but over time the glue will stain the sapphire yellow, spoiling its appearance.
Colour-change sapphires are a rare phenomenon. The gemstones can simply show different shades of blue depending on the light source, or they can change colour completely from blue-violet in daylight to red or reddish violet in artificial light.
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