饱水竹简变色原因的研究

竹简出土后由于所处环境发生了很大的变化，其颜色也随之快速的变化，竹简的变色使竹简上的字迹模糊不清，很难识读，极大地影响了竹简的史料价值。为研究导致竹简变色的原因，采用3％草酸法、1％的硼氢化钠法、3％的连二亚硫酸钠法、1％过氧化氢法、乙醇法以及控制金属离子浓度的鳌合法分别对竹简进行了脱色处理并采用红外光谱分析及X射线能谱仪对各种方法处理后的竹简进行了分析与检测。研究结果表明：(1)影响竹简变色的主要原因是竹简中的二价铁离子氧化变成三价铁离子，三价铁离子与竹材中的酚类衍生物反应生成深色化合物，导致竹简颜色变深。(2)许多发色基团在光和氧的作用下也会导致竹简变色，不过它们不会引起竹简变色过深。但金属离子尤其是铁元素的存在会加速这种变色甚至发黑。(3)用草酸处理的样品经过一段时问后之所以会出现返色的现象，是由于草酸与铁离子反应生成草酸铁，该反应强于酚羟基与铁离子的结合力，因此草酸可以起到脱色作用。草酸铁为浅黄色，这种颜色与竹材颜色相近。但草酸铁耐光性较差，当吸收紫外光时草酸铁容易发生分解，如果此时有酚类物质存在，则分解的铁离子能与之反应形成黑色物质。同时随着空气中温湿度的不断变化．竹简内部的铁离子也会不断被迁移到竹简的表面，致使竹简再度被“着色”。

Reasarch on the decoloration of waterlogged bamboo slips

The unearthed bamboo slips face great environmental changes and thus their colors change rapidly from white at the beginning, then become dark brown and finally even darker. The color - change makes the writings on the bamboo slips illegible, which have greatly affected their value as historic materials. To find out the root cause of color changes in bamboo slips, the bamboo slips were decolored by adopting 3% oxalate method, 1 % sodium borohydride method, 3 % sodium dithionite method, 1 % sodium perhydride method, ethyl alcohol method as well as the chelatometry for controlling metal ion concentrations. Then the bamboo slips were analyzed and tested that had been treated with the above methods by applying infrared spectroscopic analysis and X - ray energy spectrometry and the results are as follows: (1) The main cause of color changes in the bamboo slips is that the bivalent ferric ion changes into trivalent ferric ion, and that the trivalent reacts with phenol derivatives in bamboo materials to yield dark compounds, this leads to the dark color. (2) A lot of chromophores can also lead to the color changes of the bamboo slips under the reaction of light and oxygen, but they will not cause too dark colors. Only when there exists metal ion, especially the ferric ion, the color will change faster and even darker. (3) The reason why samples treated with oxalate would return to the previous color is that the reaction between oxalate and ferric ion to yield oxalate iron is more violent than the combination between phenolic hydroxyl and ferric ion, the decoloring by oxalate can work. The oxalate iron colors light yellow, similar to the color of the bamboo materials. However, the oxalate iron has poor sunlight resistance and liable to resolving when absorbing ultraviolet lights. If any phenolic material exists at this moment, the resolved ferric ion can react with it to produce dark materials. Meanwhile, with the constant changes of air temperature and relative humidity, ferric ions inside the bamboo slips are also continually moved to the surface of the slips and recolor the bamboo slips.