古玉沁色形成与鉴别.doc

古玉沁色形成与鉴别 古玉上的沁色，是因为玉器长期埋在土中，通过本身微量元素与土中物质的相互作用所形成的颜色变化。由于埋藏地域的土中所含物质不同，埋藏时间长短不同，所以使得玉器上的沁色也不尽相同，从而呈现出千变万化的颜色。清代的陈原心在《玉纪》中，对玉器的沁色进行了详细的分类，其中有这样一段记载:“诸色受沁之源难以深考，总名之曰十三彩”。一般来说，我国的北方土壤多呈碱性，玉器沁色多为黄色土沁，南方土壤湿润呈酸性，玉器上的沁色则多为白色水沁。 自宋代以降，仿古(作伪)风气日盛，再加之留皮、巧色工艺在玉作当中越来越多，近现代作伪者更是充分利用了这一点，给人们在古玉沁色认别上增加了许多难处。但若认真加以审视，除了综合加工工艺、刻痕特征、形制纹饰因素外，在巧色与沁色之间，也还是可以找到其中差别的: 一、边料、原生色与土沁色:前者有单色与多色两种，是在玉石成矿时形成，性质非常稳定，无沁门;而后者是入土后的次生变化，有沁门，且在沁色与 原玉色间多有明显的过渡扩散晕现象; 二、留皮、带糖与沁色、糖沁:留皮多在器物雕刻表现的突出点上，原玉带糖部分也与雕刻所要表现的主题有关;而沁色、糖沁系入土后自然形成，分布不依刻工意志为转移，不仅在突出点上受沁，且入沁过渡现象。 土古玉的自然沁象特征: 玉器受沁虽说需经百年以上才能形成，但由于入土之后所处壤质有别，时间长短不同，玉质不同，受沁程度也会有所不同:南方地湿，玉器易受沁变质;北方较干燥，受沁较浅，或有历经数千年不受沁者。但无论如何，都是有证可验的: 一、受沁时，玉器表面会遭破坏，浅者为蚀斑——起伏不平者为“桔皮纹”，深入玉中者为蚀孔——“土咬”，局部受侵蚀严重，朽烂如枯骨、膏泥者——“唐accurate to 0.0001g. Sample preparation: samples should be fully mixed. Sample volume: based on estimates of ash components, rapid sampling 2~10G, accurate to 0.0001g, the sample is distributed evenly within the Crucible, avoid compacting. [This standard applies to ash not more than 2% of starch and modified starch, hydrolysis does not apply to products, starch, oxidized and chlorine content greater than 0.2% (sodium chloride) for samples. ] Pre-ash: Watch the Crucible (as placed on ashing furnace or heating plates, Bunsen burner) until the samples completely carbonized. Combustion will produce volatile substances to avoid spontaneous combustion, spontaneous combustion can spilled from the crucible of the sample and cause losses. Incineration: once the flame goes out, instantly putting Crucible into the furnace, temperature rises to 900 c and maintain this temperature until all the remaining carbon is gone, General 1h is sufficient. And the Crucible and the residue into the dryer to cool to room temperature, and weighing, accurate to 0.000lg. [Into the crucible of dryer should not exceed four at a time]. Determination of number: the same sample to do the second rinse. 4, representation of results of calculation method for ash samples to original weight of