Forensic Science Programme, School of Health Sciences, Universiti Sains Malaysia, Health Campus, 16150 Kubang Kerian, Kelantan, Malaysia.
Forensic Sci Int. 2012 Nov 30;223(1-3):53-63. doi: 10.1016/j.forsciint.2012.07.020. Epub 2012 Sep 3.
Most of the automotive companies use cast iron for their engine blocks. Restoration of obliterated number on these iron surfaces by chemical etching is known to be quite difficult. Heating of the obliterated surface using oxyacetylene flame is an alternative recovery treatment suggested in literature and used in practice. However chemical etching has been established to be the most sensitive technique for detection of metal deformation present under stamped serial numbers. Hence, the current work investigated the suitability of some common etchants on cast iron surfaces with a view to determining the most suitable one for revealing the obliterated marks. The reagents tested were mostly copper containing Fry's reagent and its modifications. Two cast iron engine blocks (3.29%C and 3.1%C) of two cars--a Proton Saga and a Toyota--were utilized for the experiments. The engine blocks were cut into several small plates and each plate was stamped with some numerical characters at 8 kN load using Instron Table Mounted Universal Testing Machine. The depth of stamping impression varied between 0.2 mm and 0.3 mm. The stamped number was completely ground off manually using a metal file. The grounded surface was then polished smooth using emery papers and etched with a few selected reagents mostly by swabbing. Experimental results showed that a modified Fry's composition consisting of 4 5g CuCl(2), 100 mL HCl, and 180 mL H(2)O restored the number with better contrast at a reasonably shorter time. The above reagent is a slightly modified form of one of the Fry's original compositions--45 g CuCl(2), 180 mL HCl, and 100 mL H(2)O. Quite importantly the proposed reagent restored the original stamped numbers of both Proton and Toyota cars and also a Mitsubishi car that had been obliterated. The most widely used Fry's composition (90 g CuCl(2), 120 mL HCl and 100 mL H(2)O), although recovered the obliterated number, did not cause the desired contrast.
大多数汽车公司使用铸铁作为发动机缸体。化学蚀刻法来恢复这些铁表面上已被磨灭的编号是相当困难的。文献中建议使用氧乙炔火焰加热被磨灭的表面，这是一种替代的恢复处理方法，并且在实践中也得到了应用。然而，化学蚀刻已被确立为检测冲压序列号下存在的金属变形的最敏感技术。因此，目前的工作研究了一些常见蚀刻剂在铸铁表面上的适用性，以期确定最适合揭示已磨灭标记的蚀刻剂。测试的试剂主要是含有 Fry 试剂及其改性剂的铜试剂。两个汽车的两个发动机缸体（3.29%C 和 3.1%C）——一个普锐斯和一个丰田——被用于实验。发动机缸体被切成几块小板块，每个板块都在 Instron 台式万能试验机上以 8 kN 的负载冲压一些数字字符。冲压印记的深度在 0.2 毫米到 0.3 毫米之间变化。使用金属锉手动将冲压号码完全磨掉。然后使用砂纸将打磨后的表面打磨光滑，并使用几种选定的试剂进行蚀刻，主要是通过擦拭。实验结果表明，一种由 4 5g CuCl(2)、100 mL HCl 和 180 mL H(2)O 组成的改良 Fry 配方在较短的时间内恢复了更好对比度的号码。上述试剂是 Fry 的原始配方之一的改良形式——45 g CuCl(2)、180 mL HCl 和 100 mL H(2)O。非常重要的是，该提议的试剂恢复了质子和丰田汽车以及已被磨灭的三菱汽车的原始冲压号码。最广泛使用的 Fry 配方（90 g CuCl(2)、120 mL HCl 和 100 mL H(2)O）虽然恢复了已磨灭的号码，但没有产生所需的对比度。
