Gem facets

By | October 12, 2019

The beauty of gemstones hold certain fascinations for man, whether in raw form or faceted. In order to improve and reveal the best of a gemstone, man has gone a step further by cutting or faceting it.

Although there is no actual record on who first started gem-cutting, it certainly took many years to perfect the technique. The first step to “treatment” of gemstones is to transform them from their raw form to faceted gemstones that display the beauty, colour and brilliance.

Shortage, increase in demand and high mining costs of natural gemstones have again encouraged man to manufacture replacements or treat their natural gemstones.

Synthetic ruby was first commercially manufactured in the early 1900s by a French professor, Verneuil. Since then, many countries with advance technology in crystal growing have produced many kinds of synthetics with different growth methods, such as Flame fusion, Flux grown, Hydrothermal growth and czochralski (pulling) growth.

There are many synthetic stones available today, including synthetics of sapphire, emerald, amethyst, garnet, quartz, jadeite, diamond, spinel, alexandrite, etc. Treatment to enhance the colours of gemstones was rapidly developed in the mid-seventies. Here, enhancements of ruby, sapphire, emerald and jadeite are explored with highlights of how modern jewellers and a new breed of gemologists cope with the ever increasing synthetics and treatments manufactured in the gem market.

Major ruby producing countries include Thailand, Myanmar, Sri Lanka, Kenya and India. Burmese ruby is highly priced for its rich “pigeon blood” red or a more pinkish colour called “cherry red”. The best Burmese rubies have a distinctive glow especially in broad daylight. According to an eminent gemologist from the Gemological Institute of America (GIA), the glow is the direct result of fluorescence.

When fluorescent stones are struck by ultra violet rays, a strong component of sunlight, they excite atoms within. Thai rubies almost always lack the vibrancy of their Burmese counterparts. This is due to the presence of iron, which inhibits fluorescence.

Since the Socialist government took over Myanmar (Burma) in 1962, the mining of rubies has slowed down and most gems are mined illegally and smuggled out of the country. Today, the term Burmese ruby no longer indicates its origin but is synonymous with the ideal beauty in the gemstone.

On the other hand, the excitement of the discovery of Burmese look-alike rubies in Vietnam has been short-lived when the government imposed a ban on the export of the rough gems.

In Thailand, heat treatment is used to alter the iron concentration to reduce the purple and brownish colours of the rubies. This process does not help the Thai rubies to look like their Burmese counterparts. Heat treatment may improve the colour of rubies but it also obliterated some of the characteristic inclusions that gemologists need for identifying the country of origin of the gemstone.

Blue Sapphire
The best blue sapphire is said to come from Kashmir, India. A good quality blue sapphire has that velvety blue known in the gem trade as “sleepy” or other descriptive term referred in India as “peacock’s neck”.

The Kashmir sapphire is so rare that well-known jewellers have difficulty getting them for their royal customers. The reason for the rarity is the closure of the mine near the sensitive border state between India and China. Presently, there is no shortage of blue sapphires as Sri Lanka and Burma are also producers of good quality blue sapphires.

In the mid-seventies, the Thai gem dealers found a formula to improve the colour of the otherwise useless milky rough sapphire called geuda used by the Sri Lankan native as foundation for buildings, rock gardens, etc. Heating geuda to 1800 degrees Celsius releases the natural colour locked within the geuda and turns it into a more desirable blue sapphire. Like their Sri Lankan counterpart, sapphires found in Australia, Africa and Thailand are also being treated in the same manner.

In order to meet the increasing demand, manufacturers discovered a new form of heat treatment that has created a lot of controversy. Instead of allowing the natural colour from within the stone to colour the stone during heating, an artificial colouring agent is added and allowed to diffuse a few micron into the otherwise colourless sapphire. If a diffuse treated blue sapphire is recut, it is very likely to lose its colour.

It is considered a fraud if the jewellers who sell diffused treated ruby or blue sapphire do not reveal the truth to their customers.

The finest emerald of medium-dark green comes from Columbia. Other countries that produce emeralds are Zambia, Pakistan, India and Brazil.

Emeralds from Zambia has a tint of gray or blackish tone while the colour and lustre of emeralds from Pakistan is said to be similar to its Columbian counterpart.

Virtually all emeralds bear natural inclusions, often considered distinctive though undesirable if too numerous. If the flaws reach a finished emerald’s surface, they can be masked with oil.

Emeralds are soaked in a heated cedar wood or palm oil in the pressure chamber. The pressure helps to drive the oil further into their cracks but unfortunately oil evaporates or seeps out within a year.

Jadeite possesses an extremely transparent appealing green, most of which comes from Burma. Good quality jadeite is very rare. As a result, manufacturers turn to other ways to improve the colour of the jadeite.

The most common technique is to dye the gem with a green dye. Another technique, bleaching, where a strong acid is used to dissolve the iron oxide or impurities from the jadeite is also used. Whilst it enhances the appearance of the jadeite, this method also weakens the structure of the gem.

To strengthen the bleached jadeite, the manufacturer coats the material with a layer of colourless plastic. Through wear and tear, the jadeite will reveal the true nature of its original colour.

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