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Jade, a gemstone with a long history

Jade, a gemstone with a long history - September 2011 - n. 02
Jade, a gemstone with a long history - September 2011 - n. 02
Jade is a word with a long tradition behind it, a word which is still erroneously used in many cases commercially today as a generic term to describe a number of massive, translucent minerals suitable for carving. However gemmology distinguishes between jadeite and nephrite jade, two types of jade that in mineralogical terms are only similar because they both belong to the large family of silicate minerals. It was the French professor A. Damour who scientifically determined in 1863 that what we called jade was actually two different minerals: jadeite and nephrite. When Damour realised that the green Burmese mineral he was analysing was different from what was commonly called Chinese jade (nephrite), he called it jadeite.
Both minerals are extremely tough thanks to their generally dense compact mass of interlocking microcrystals. Toughness is the physical characteristic which prevents breakage, with jade being the toughest known mineral.
It is extremely difficult to break because its compactness and this makes it particularly suitable for carving.
Jadeite is a piroxene mineral. In nature it is typically found in extremely compact polycrystalline aggregates (monoclinic crystal system) which make it either translucent or opaque. In exceptional cases jadeite is found in monocrystals, an extremely rare and very valuable material. Top quality emerald green jadeite was called “imperial jade” because it was so sought after by the Chinese emperors. Jadeite comes in several colours, not only in green. It is found in both uniform white, black, yellow, orangy-red, brown, grey, light purple, lavender and mauve, combinations of these colours and streaked or spotted colour schemes. Clever carving when it comes to choosing style and shape can make the most of its natural colours.
Colour is largely affected by the presence of trace elements which were incorporated into the mineral as it was formed. For example bright green comes from the presence of chrome, while lavender is caused by transfer ferrous-ferric state of iron. Other colours are due to residual elements or compounds dissolved in water which at some point infiltrated the spaces between the granules of the polycrystalline mass.
Emerald green jadeite, or imperial jade, mined in Myanmar, is the rarest and most sought-after type of jade. In order to be classified as “imperial”, it has to be semi-diaphanous, emerald green and completely inclusions free. Its worth rivals that of diamonds.
Although the various shades of green jade are better known in the West, in the Far East white or yellowish white jade with a hint of pink is also highly prized. Red jade is again one of the most valuable varieties. Lavender jade is a popular choice for pieces of jewellery.
The main source in terms of quantity and quality has always been Myanmar (formerly known as Burma). Myanmar is better known for mining and exporting raw jadeite rather than working it. It is worked in China, with the finished pieces being exported all over the world.
In the USA the “Tom Lantos Block Burmese JADE Act” prohibited the importation of Burmese gems, either raw or worked, from 2008 as a protest against the serious violations of human rights committed by the Burmese military government. In 2009 the US customs published their Conditions for Importation, the regulations that governed the application of the Jade Act. The JADE Act specifies that all rubies, jadeites and jewellery containing these gems from Myanmar may not be imported into the USA, even if the stones have been worked elsewhere. Exceptions are only applied for stones already in the US before 27 September 2008 and for articles imported for personal use.
The CIBJO (Confédération internationale de la bijouterie, joaillerie, orfèvrerie, des diamants, perles et pierres - The World Jewellery Confederation) has adhered to the United Nations Human Rights Council Resolution S-5/1 passed on 2 October 2007 and therefore invites its associates not to purchase gems from Myanmar.
Over the last few decades jadeite’s attraction has been slightly tarnished by the diffusion of enhancement treatments for low quality, low cost jadeite. These treatments make low quality jadeite an attractive buy on the mass market, but it is undoubtedly a deceptive material. Enhancement techniques and processes took a jump forward in 1983, when a large quantity of low grade jadeite requiring treatment known as 83-jade was discovered in Myanmar.
This led to a classification of jadeites being stipulated in Hong Kong, world capital of jade trading, to distinguish natural stones from treated material.
A-jade: natural jadeite that has not been treated in any way except for surface waxing with wax or paraffin. Acids may be sparingly used to remove residual material after abrasion.
These operations are considered a normal part of the traditional working of the material.
B-jade: treatment involves exposing a promising, but stained, piece of jadeite to chemical bleaches and/or acids and impregnating it with a clear polymer resin to fill the gaps left by the action of the acids.
C-jade: has been artificially stained or dyed. The artificial colouring does not last.
B+C-jade: jadeite that has been both artificially dyed and impregnated.
D-jade: a doublet comprising a green jade top with a translucent plastic backing.
Oriental peoples believe that only A-jade retains its mystic significance. In the West aesthetic values prevail and B-jade is admissible; indeed it is much appreciated because of its translucent qualities. Nephrite may occasionally be stained or dyed. Polishing with paraffin is a common practise which is allowed by the market.
The evaluation of finished jadeite jewellery is based on the following parameters: colour, clarity, cut, size, translucence, texture. At an auction in Hong Kong in 1997 an “imperial” jadeite necklace of 27 grains, each roughly 15 mm in diameter, was sold for 9.3 million dollars, while a pair of “imperial” jadeite drop earrings with rose-cut diamonds was sold for 1.55 million dollars.
Nephrite is not an intrinsically expensive stone. Its value lies principally in the quality of the carving and its antiquity.

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