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Subject:Re: calcification and oxidation in jade Posted By: LEE <leileezhang@yahoo.com> Tue, Mar 16, 2010 IP: 202.174.35.14 90% of jade pieces that have been buried for several hundred years, would have some sort of surface alteration or patina. The amount of patination would depend on rainfall. the more humid areas will have more patina. The sort of patina will depend on the minerals in the soil. Russet patina if the ground if high in iron oxide. Black patina if the ground is high in organic material and whitish patina if the area is high in calcium.
The other point on the finish of the carving. Old carving have a satin like finish because they were polish with crude abrasive, usually powdered garnets? Burial of the jade will also cause some surface alteration like micro calcification will further reduce the gloss on the surface. Modern polishing material like Aluminium oxide can create a high gloss. Such reflective high gloss pieces will date to 20th century or latter. It is safe to say that a glossy piece is modern unless the antique piece is repolished which is possible in some pieces in Western collection, where nicks and chips are polished back.
Subject:Re: calcification and oxidation in jade Posted By: Samuel <samuelwong@artofasia.cn> Wed, Mar 17, 2010 IP: 67.159.44.51
90% of jade pieces that have been buried for several hundred years, would have some sort of surface alteration or patina. The amount of patination would depend on rainfall. the more humid areas will have more patina. The sort of patina will depend on the minerals in the soil. Russet patina if the ground if high in iron oxide. Black patina if the ground is high in organic material and whitish patina if the area is high in calcium.
-No, jade is too valuable to be buried with the dead. And majority of archaic jade were passed down to next generation.
++++++++++++++++++++++++++++++++++++++ The other point on the finish of the carving. Old carving have a satin like finish because they were polish with crude abrasive, usually powdered garnets?
-No. In Neolithic Period the stone mortar was used for grinding millet grain to make bread, and there are many holes at the mountain foot in North China where the stone floor of the hill were drilled to make mortar for grinding millets grains. That thing was applied to grind CORUNDUM (hardness 9) and quartz (hardness 7) into powder. The abrasive agent have 2 kinds, the crude one used for smoothing after jade was cut into figure, then the powder one use for shining and polishing jade. These 2 minerals are hard but crispy, and easy to break.
*garnet has hardness of 6.5-7.5 and garnet mine in China located in Fujian Province, impossible to be transported to the north to make archaic jade, but corundum and quartz are widely available in the north east.
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Burial of the jade will also cause some surface alteration like micro calcification will further reduce the gloss on the surface. Modern polishing material like Aluminium oxide can create a high gloss. Such reflective high gloss pieces will date to 20th century or latter. It is safe to say that a glossy piece is modern unless the antique piece is repolished which is possible in some pieces in Western collection, where nicks and chips are polished back.
-Corundum is the most common naturally occurring crystalline form of aluminium oxide which were widely used to polish jade since “Neolithic Period”. And there is a legend said in the record of Sima Qian the grand historian of China said that in the spring and autumn period there was small knife/chisel that can easily cut jade as cut melon, and that knife/chisel is surly a diamond imported from the west. And diamond was crushed into powder to shine jade. Diamond was not a valuable mineral at that time. Burial jades depend upon the tombs and their environments, Shang to Han tombs are mostly 15 meters under the ground with chamber covered by timbers, fabric, stone, sand and charcoal. Some tombs were collapsed, some flooded, some don’t, and some were looted shortly after tombs were sealed. And robbers searched mostly for jade and gold. Nephrite is the toughest and tightest mineral on earth it resists to any natural toxic, acid, alkaline from the tombs and earth layers. However, modern strong chemical would corrode nephrite within a minute.
And how can you explain “glossy” polish of the Han jade burial suit, Ming plaque, and water dropper? Were they made in 20th century?
*Image copyright Gary L. Todd, used by Permission'
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