The most of natural high-quality red jadeites are too small to be gemstones, so the heat treatment in the market is very common. Heat the deep-red one at a high temperature to turn it into a bright red. How do you identify the red jadeite that has been treated with color? Why does the color change when heated at high temperatures？
The bright red color of heated red jadeites is due to the process of water loss of limonite.with water loss speeding up，the limonite turns to hematite.
It is not easy to identify the heated red jadeites by using normal methods，but the appearance of heated sample is drier than the nature one.Also，we can test the sample with FTIR.The natural red jadeites have the absorption peak of crystal water and absorbed water at 1500～1700、3500～3700cm-1.
The red jade on the market is mostly produced from low-value yellow or brown-yellow jadeite, which contains limonite (FeO(OH)·nH2O) and the coloring element is Fe2+. The jadeite is accompanied by the oxidation process of Fe2+to Fe3+in the heating process, and the limonite material loses the adsorbed water and transforms into goethite or lepidocrocite, then the goethite loses the crystal water and transforms into hematite, which leads to the bright red appearance of jadeite.
The infrared spectroscopy absorption peak shape of natural red jadeite and color-treated red jadeite changed from U-shaped before heating to V-shaped after heating, and the specific absorption line also changed slightly.
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