紫外荧光法检验激光打印文字朱墨时序

Determination of Crossing Sequences Between Laser Printed Text and Seal Impression by Ultraviolet Fluorescence

目的研究如何运用紫外荧光检验激光打印文字与盖印印文的形成时序,为鉴别此类案件提供新的、无损、快速、可靠的检验方法。方法使用VSC5000文件检验工作站,采用不同紫外光对72份实验样本进行照射和透射检验,并调整滤色片、对比度、亮度等参数,观察"先朱后墨"和"先墨后朱"两种时序条件下的荧光反映。结果两种时序条件下,打印文字与盖印文字交叉处的荧光反映存在较大差别。在先墨后朱时序下,打印文字在交叉处笔画颜色变深、宽度增加,但能保持相对完整;在先朱后墨时序下,打印文字在交叉处笔画颜色、宽度没有变化,但部分笔画可能存在中断或不完整现象。结论运用荧光法能准确判定激光打印文字与盖印印文的形成时序,该方法可应用于实践案件鉴定工作。

Objective This paper aims to demonstrate a new, non-destructive, quick and reliable way for determining crossing sequence of laser printed text and stamped seal impression using ultraviolet fluorescence. Methods A Video Spectral Comparator （VSC5000） was applied. 72 document samples, prepared with 6 brands of laser printer and 3 types of inkpad, were examined under ultraviolet light with adjustment of parameters including color filter, contrast, brightness and others. Then fluorescence reflection on overlapping region of seal impression and printed text was observed. Results There was great difference at two crossing sequences, that is, printed text over seal impression and seal impression over printed text. In the crossing region of seal impression over printed text, the text was darker and wider, but the strokes maintained continuous and complete. In the crossing region of printed text over seal impression, the text kept the same color and width with those separated from the stamp impression, but some of them were interrupted or incomplete. Conclusions The ultraviolet fluorescence method is a very effective and attractive technique for determining the sequence of laser printed text and stamped seal impression. Some challenging samples such as year-long documents, unclear stamps, and those not covered yet here, can be detected in further study.