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Monday, 4 November 2013

Jade Authentication

Depicted from Origins of Chinese Art and Craft
        
        The ancients laid down five criteria in authenticating jade articles: warm, moist and glossy; uniform veins both inside and outside; clear and clarion sounds; hard and dense; and clean and pure in colour. Modern authenticators follow five. They are:

1. Jade Texture
        Smoothness and fineness come first in jade authentication. This is what sets jades apart fundamentally from common stones. The smoother and finer the jade is, the purer it is.

2. Jade Hardness
        Hardness is also an important criterion. This can be measured by scratching or cutting. Without a hardness meter, we may use some substitutes for references. For example, one degree of hardness applies when the surface can be scratched with a piece of paper; 2.5 degrees corresponds to that of our nails; 3.5 degrees equals to that of copper; 5.5-6 degrees, glass and 6-7degrees, steel knife.

3. Transparency
          The transparency is proportionate to texture. The higher the transparency, the smoother and finer it is. A high transparency can also enhance the colour. There are four degrees for measuring transparency:
  • Transparent: amber, brown quartz and crystals;
  • Sub-transparent: agate and rose quartz;
  • Translucent: jade and emerald;
  • Opaque: malachite and turquoise.
4. Specific Gravity of Jade
           Jade’s specific gravity ranges between 2 and 3. Frequently used methods for measuring its specific gravity include balance method, pycnometer method and the method of specific gravity solution.

5. Jade Colours

        Colours of jade result from its mineral elements. For example, jade green is caused by the content of chrome while pea green and deep green are attributable to iron oxide. For common jadeite, pure jade green is important, and its price is related incrementally to its degree of density, purity, evenness and regularity. For white jade, top quality means tallow white.

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