馆藏金属器物上浅蓝色铜锈蚀物的辨别与成因分析

Identification and interpretation of pale blue copper corrosion products formed on metal objects in museum collections

不同于新出土青铜器上的锈蚀物,博物馆藏金属器物上经常可见浅蓝色铜的锈蚀物。为辨别和探析其成因,通过采用扫描电子显微镜-能谱仪(SEM-EDX)、X射线衍射仪(XRD)和激光拉曼光谱仪(Raman)进行元素成分和物相综合分析,发现其为铜的有机盐。这些有机盐包括简单(或碱式)的甲酸铜和乙酸铜,也包括复杂的含有钠离子和碳酸根的乙酸铜NaCu(CO3)(CH3CO2)、含有钠离子和氧离子的水合甲酸铜Cu4Na4O(HCOO)8(OH)2·4H2O。这种浅蓝色铜的有机盐形成根源主要有两种:储存或展览环境的不当;用于除锈的化学试剂的残留。要杜绝这类锈蚀物的形成需要确保储存和展览器物的环境低湿度且无有机酸释放材料的存在。对经过化学处理的器物应确保将化学试剂清理干净且无任何残留以绝后患。对复合材料器物的处理更应谨慎,因为对不同材质的处理和保存环境要求不一样,要个例对待。

Different from corrosion products on freshly excavated bronzes,pale blue copper corrosion products have often been observed on metal objects in museum collections.These were identified by a combination of scanning electron microscopy-energy dispersive X-ray spectrometry(SEM-EDX),X-ray diffractometry(XRD)and Raman spectrometry as copper organic salts including simple(or basic)copper acetate and copper formate,as well as some complex compounds such as sodium copper carbonate acetate NaCu(CO3)(CH3CO2)and sodium copper formate hydroxide oxide hydrate Cu4Na4O(HCOO)8(OH)2·4H2O.The formation of this type of copper corrosion product was caused by poor environment of display or storage and/or residual chemicals used in previous conservation treatments.To prevent formation of these compounds,the objects need to be displayed or stored in an organic acid-free environment with controlled low relative humidity.Chemicals used for conservation treatment should completely be removed from the objects to prevent further deterioration.One needs to be especially cautious to treat and preserve objects with composite materials,as different environmental conditions are required for the safe preservation of different materials.For this reason,such objects should be treated and preserved on a case by case basis.