Yin Siaw Hui, Kuppuswamy R
Forensic Science Programme, School of Health Sciences, Universiti Sains Malaysia, Kampus Kesihatan, 16150 Kubang Kerian, Kelantan, Malaysia.
Forensic Sci Int. 2009 Jan 10;183(1-3):50-3. doi: 10.1016/j.forsciint.2008.10.009. Epub 2008 Nov 28.
Chemical etching, which is the most sensitive method to recover obliterated serial numbers on metal surfaces, has been practised quite successfully in forensic science laboratories all over the world. A large number of etchants suitable for particular metal surfaces based on empirical studies is available in the literature. This article reviews the sensitivity and efficacy of some popular etchants for recovering obliterated marks on medium carbon steel (0.31% C with ferrite-pearlite microstructure) used in automobile parts. The experiments involved engraving these carbon steel plates with some alphanumeric characters using a computer controlled machine "Gravograph" and erasing them to several depths below the bottom of their engraving depth. Seven metallographic reagents of which most of them were copper containing compounds were chosen for etching. The erased plates were etched with every one of these etchants using swabbing method. The results have revealed that Fry's reagent comprising cupric chloride 90 g, hydrochloric acid 120 mL and water 100mL provided the necessary contrast and was concluded to be the most sensitive. The same reagent was recommended by earlier workers for revealing strain lines in steel surfaces. Earlier, another reagent containing 5 g copper sulphate, 60 mL water, 30 mL (conc.) ammonium hydroxide, and 60 mL (conc.) hydrochloric acid was proved to be more sensitive to restore erased marks on low carbon steel (0.1% C with ferrite-pearlite structure) [M.A.M. Zaili, R. Kuppuswamy, H. Harun, Restoration of engraved marks on steel surfaces by etching technique, Forensic Sci. Int. 171 (2007) 27-32]. Thus the sensitivity of the etching reagent on steel surfaces appeared to be dependent on the content of carbon in the steel.
化学蚀刻是恢复金属表面被抹去序列号最灵敏的方法，在世界各地的法医学实验室中都有相当成功的应用。基于实证研究，文献中有大量适用于特定金属表面的蚀刻剂。本文综述了一些常用蚀刻剂对汽车零部件中使用的中碳钢（含碳量0.31%，铁素体-珠光体组织）上被抹去标记的恢复灵敏度和效果。实验包括使用计算机控制的“格拉沃格拉夫”机器在这些碳钢板上刻上一些字母数字字符，然后将它们擦除至刻痕深度底部以下的几个深度。选择了七种金相试剂，其中大部分是含铜化合物用于蚀刻。使用擦拭法用这些蚀刻剂中的每一种对擦除后的板材进行蚀刻。结果表明，由90克氯化铜、120毫升盐酸和100毫升水组成的弗莱试剂提供了必要的对比度，被认为是最灵敏的。早期的研究人员也曾推荐使用相同的试剂来显示钢表面的应变线。早些时候，另一种由5克硫酸铜、60毫升水、30毫升（浓）氢氧化铵和60毫升（浓）盐酸组成的试剂被证明对恢复低碳钢（含碳量0.1%，铁素体-珠光体结构）上被擦除的标记更灵敏[M.A.M.扎利、R.库普斯瓦米、H.哈伦，通过蚀刻技术恢复钢表面的刻痕，《法医学国际》171（2007年）27 - 32]。因此，蚀刻剂在钢表面的灵敏度似乎取决于钢中的碳含量。
