古玉沁色形成与鉴别

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 烂斑”(因唐代及以前土古玉上常见，故有此称);其不可人为作伪者有三: (1)蛀蚀孔呈外小内大的不规则状，孔内有如纤维网;

(2)蛀孔周围有一白化过渡层;

(3)蚀孔或裂绺内或有砂粒(质硬未风化者)，或有均质胶固体;

二、凡玉质较脆弱的纹路或裂绺处更易受沁，形成沁纹——颜色较深，且有向周围扩散之势，且沁纹多呈凹陷现象。古玩界，对不同沁纹现象分别有不同称谓:

(1)牛毛纹:沁纹呈同向排列，状如牛毛般细密;

(2)乱柴纹:沁纹如树枝状结构延伸;

(3)蚂蚁脚:沁纹呈不规则网状，细如蚁迹;

(以上沁处，抚之无痕，在20倍放大镜下，均可见凹陷现象;而人为火烧纹，纹路生硬，大多如放射状)

(4)钉金沁:受沁处呈点状凹陷，铁锈般的黄褐沁色沉积，有如钉状，是高古玉的独有表征之一;

三、凡部分受沁者，其沁色自然由深及浅，很有层次感——扩散沁色现象，尤其是在受沁与不受沁处之间、表里之间、此一沁色与彼一沁色之间，更易分别(唯一例外的是，水银沁有呈块状，而与周围沁色截然分明者)，至于比较好的玉质，从“开窗见地”处往里看，沁层更有立体感;

四、如果是“彩沁”，沁纹与蚀斑处通常更为明显，呈色深浅层次有很自然;两种以上沁色，常会发生颜色取代与覆盖现象，比如黑色覆盖红色、红色取代土沁色、水沁覆盖糖沁色等;

五、自然沁色在器表呈连续分布时，不会因刻痕而中断，否则即有“老玉新工”之嫌;

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