'Jade', or yu, as it is called in China, is strictly speaking a generic term for two different gems, nephrite and jadeite. The name is derived from the Spanish piedra de ijada, loin-stone, jade having been recognised by the Amerindians as a remedy for kidney ailments. Because of its beneficial effect on the kidneys, the stone was also known as lapis nephriticus. That, indeed, is where the term 'nephrite' came from.
Jadeite and nephrite are both regarded in China as zhen yu, 'genuine jade'. It was not until the beginning of the 19th century that mineralogists and gemmologists started to differentiate between them, since they bear a considerable resemblance to each other in terms of their appearance, their hardness and the properties they exhibit when being processed. Both are tough, since they consist of dense, close-grained, matted aggregates, but they differ from one another in their chemical composition and colours.
Nephrite ranges mainly from mid to dark green or grey-green, but it can also be white, yellowish or reddish. Rarer, and somewhat tougher, jadeite displays hues which include green, but also white or pink, and reds, blacks, browns and violets. In both minerals, the way the colour is distributed varies a great deal. Only in the very finest jade is the colour evenly distributed. Both nephrite and jadeite often have veins, blemishes and streaks running through them, though these may not always be regarded as flaws. On the contrary, some of these patterns are considered particularly valuable.
Jade: from raw material to finished product
Jadeite is rarer than nephrite and is therefore regarded as more precious. Nephrite deposits have been found in China, New Zealand, Russia, Guatemala and the Swiss Alps. Dark green jade, so-called Canada jade, is also found in Western Canada. Jadeite is found in China, Russia and Guatemala, but the best stones come from Burma, now known as Myanmar. There, at the annual 'Gems, Jade and Pearls Emporium', blocks of jade in all sizes are auctioned.
When purchasing the raw materials, the dealers need to be fairly lucky, since the nodules, blocks and fragments are sold either whole or after having been cut into slices, and there is only a very small window, the result of some initial grinding. So the buyer cannot see exactly what is hidden on the inside: valuable green jade, or an almost worthless, speckled or streaky material. It is not until the cutting process begins that the real quality is revealed.
In the jade-cutting centres of Canton, Beijing and Hong Kong, the raw material is processed with carborundum and diamond powder. Since jade is, as a rule, not transparent, but has a fine lustre, the cabochon is the form best suited to it. Thin slivers, which can be worn as pendants, and jade bracelets are popular too. Round, cylindrical and flat shapes can be combined to make attractive necklaces. Traditionally, jade is processed into slender figures, filigree images or thin-walled vessels. This is sometimes erroneously referred to as jade carving. Unwanted material is in fact removed during the cutting process, and the stone is subsequently polished. Here once again we see the subtle difference between nephrite and jadeite: whilst polished nephrite has a surface with a resinous lustre, the glassy lustre of jadeite after polishing seems to shine almost like that of a mirror.
