閃玉仿古實驗之白化生成機制探討

玉是中國文化重要的表徵，在華人的歷史社會中扮演著重要的角色。中國文化中所用之真玉即為閃玉，故閃玉之考古研究對中國古玉文化來說，有其主導之地位與歷史意義。許多出土的閃玉質古玉會因為風化作用而呈現白化的現象，其白化所代表的科學意義在考古界中亦頗受重視。由於古玉的價位通常不斐，近代亦出現許多仿古玉器，仿製的與天然白化的區別，亦成為考古界或古玉收藏玩家的重要課題之一。目前一般市面上玉器仿古白化的方法主要為酸處理、鹼處理及熱處理，因此本研究主要探討在酸、鹼處理及熱處理作用之下，各階段新鮮閃玉樣品外表白化的情形、表面的顯微結構變化，元素於酸、鹼溶液的溶出情形，並以拉曼光譜非破壞性的分析來建立在酸、鹼處理及熱處理下的閃玉拉曼光譜資料。研究結果顯示，閃玉白化的程度會和泡酸的時間成正比，並造成表面結構的破壞。分析酸溶液中的元素陽離子(Ca、Mg、Fe)總溶出量高於Si離子，而各種離子的溶出率會隨著泡酸的時間而增加，且硫酸溶出之元素總量比鹽酸高，得知硫酸對於閃玉之破壞較強。相對於酸處理，鹼處理方面則較無明顯之結果，於外觀亦無白化生成。泡酸後的樣品以拉曼光譜分析發現有些微脫水的現象，刮取泡酸五個月後之樣品表面白化生成物，經XRD檢測為低溫石英。在閃玉白化的程度會隨著加熱溫度增加成正比，並且於表面會產生裂隙，且裂隙亦隨溫度上升而加大。而受新鮮閃玉樣品內含雜質(鐵)量的影響，加熱後會呈紅棕色的外觀色澤。經由拉曼光譜與X光繞射分析檢測發現，閃玉樣品會因加熱而產生脫水作用，而轉變為透輝石礦物相。

關鍵字

閃玉；白化；酸處理；鹼處理；熱處理；拉曼光譜

並列摘要

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℃.

並列關鍵字

Nephrite ； whiten ； Acid treatment ； Base treatment ； Heat treatment ； Raman spectroscopy

參考文獻

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[27] M. Whittels, “Structural transformation in amphiboles at elevated temperatures,” American Mineralogist（36）, 1951, pp. 851.

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閃玉仿古實驗之白化生成機制探討

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