The study of whitening mechanism of fake nephrite archaic jades

• Main Authors: Chin-Lung Liu, 劉金龍
• Other Authors: 余炳盛
• Format: Others
• Language: zh-TW
• Published: 2006
• Online Access: http://ndltd.ncl.edu.tw/handle/d3wf7t

碩士 === 國立臺北科技大學 === 材料及資源工程系所 === 94 === Jade, a Chinese culture important token, plays important role in the Chinese history. Although there are many minerals and rocks have been reported to be used as raw materials of archaic jades, the nephrite is always the most precious and important one. Many nephrite archaic jades became whitened due to weathering. This whitening phenomenon has not only archeological but also scientific significances. Nevertheless, fake archaic jades which were made via acid/base/heat treatments have become popular in the market for the high value of true archaic jade. To distinguish the fake whitened nephrite jades from the natural ones becomes a challenge to archeologists and antiquaries. This study mainly inquires into the reactions of nephrite during different conditions of acid/base/heat treatments, to find out the characteristics of fake whitened nephrite jade. The surface structure, whitening conditions of nephrite and elements dissolution in acid/base solutions are examined. Non-destructive Raman spectroscopy is also used to observe their crystal structure changes in each stages of treatments. The result indicates nephrite can be easily whitened with acid treatment, and the degrees of whitening, surface structure breakage and total amount of ion dissolved in solutions are proportional to the time of acid treatment. The amount of cation (Ca, Mg, Fe) dissolved from nephrite is higher than that of Si ion. The higher dissolution of nephrite in sulfuric acid than that in hydrochloric acid indicates the former has stronger erosive ability to nephrite than the latter. Opposite to acid treatment, no whitening phenomenon and surface structure change could be observed on the ammonia water treated nephrite. The Raman spectrum indicates slight dehydration occurred on the surface of acid-treated nephrite. XRD analysis shows the compositions of the white powder scraped from the acid treated nephrite contain α-quartz in addition to nephrite. The color of nephrite change from green to lightly green, grayish white, and light yellowish brown when be heated to 650, 850 and 1050℃ respectively. The yellowish brown color might be caused by the ferric ion which was oxidized from ferrous ion during the heat treatment. Surface cracks of heat treated nephrite could be observed under SEM. The analysis of Raman spectroscopy and XRD indicate the nephrite will be dehydrated and transformed to diopside under the heat treatment above 950℃.