Studies Of Infrared Spectra On The Amber And Its Imitation

The samples of the natural, optimized and treated amber and its imitations wereanalyzed with some nondestructive testing (NDT) methods, such as IR and conventionalgemological instrument. Then the natural amber and its imitations were heated underdifferent pressures. The parameters of the heated samples at different pressures weremeasured and credible NDT methods were put forward to identify the samples.Amber is a very precious gemstone, so many kinds of optimizing ambers, treatedambers and its imitations were appeared in the markets. It is a difficult problem for theconsumers, jewelers and identification institutions to identify the amber from its imitationswith NDT methods. In order to solve the problem, the optimizing amber, treated amberand imitated amber were tested with the methods, such as FTIR, spectra and indexmeasurement, etc. Methods were provided for identifying the imitated amber such ascopal. The optimized amber and treated amber still cannot be identified with the NDTmethod mentioned above. In order to distinguish optimized and treated amber from thenatural ones the samples were heated at different pressures.The amber and copal were heated at one atmospheric pressure. When the amber washeated, the ratio of A to B of the infrared spectra changes regularly, in which peak A isresulted from the asymmetrical stretching vibration absorption of aliphatic carbonhydrogen bonds and B is in virtue of the stretching vibration absorption of carbon oxygendouble bonds. Besides, the imitation copal was heated to different temperature, and theabsorption peaks νC-H(the carbon hydrogen in olefinic bond asymmetrical stretchingvibration weak infrared absorption peak), νC=O(the carbonyl group in unsaturatedcarboxylic acid stretching vibration strong infrared absorption peak) and δC-H(theunpolymerized terpene in aromatics out-of-plane bending vibration weak infraredabsorption peak) changes regularly at different temperatures. When the copal was heatedto the critical point at which the unpolymerized terpene in aromatics volatilized, theinternal structure was destructed and the appearance characteristics had been different.The NDT parameters of the optimized amber were almost the same with the amber whichwas heated under ordinary pressures.The copal was heated under different pressures. The FTIR absorption peaks weredifferent from the heated copal which was heated under atmospheric pressure. As thepressure increase, the νC-H, νC=Oand δC-Hof the infrared spectra absorption peaks changesfaster than that under atmospheric pressure, and the νC-H, νC=Oand δC-Habsorption peakswere almost disappeared at150to180degree centigrade. When νC-H, νC=Oand δC-Hwere disappeared, the FTIR absorptions of copal were same with that of the optimized ambers.