The Research On Sequential Identification Of Crossed Laser Printed Text And Seal By Polarized Optical Microscope

The sequence of crossed stamp impression and text is a very important aspect in the field of document examination,but also a more difficult problem in the examination and identification at the same time.In recent years,laser printers have come into people's daily work and life,and the illegal and criminal activities related to laser printing documents are also increasing.Therefore,it is of great significance to study the methods of examination and identification for the sequence of laser printed text and seal.In this paper,a systematic experimental research on the examination of the sequence of laser printed text and seal is carried out by polarized optical microscope for the first time:(1)Five different types of laser printers were selected through the microscopic morphology of printed characters observed by microscope,and fifteen different types of inkpad and ink were selected by using Raman spectroscopy to analyze pigments,which were used for making samples.(2)Polarized optical microscope was used to examine different types of samples,so as to study the microscopic characteristics of the first printing and then stamping as well as first stamping and then printing,and summarize the law of characteristics.(3)By the diachronic examination of samples with sequencing of stamping and printing,the changes of microscopic characteristics were studied at the intersection of stamping and printing,in order to explore the influence of sample preparation time on the results of examination.(4)A comparative study was made on the effects of polarized optical microscope,ordinary microscope and fluorescence microscope in examination for laser printed characters and sequencing of stamping and printing.The experimental results indicates that:(1)There were some differences in the polarizing microscopic characteristics between laser printed characters and sequencing of stamping and printing,so we could use the polarized optical microscope to determine laser printed characters and sequencing of stamping and printing.It was easy to determine the sequencing of stamping and printing for print characters with dense and porous ink powder;it was difficult to determine the sequencing of stamping and printing for print characters with dispersed ink powder,but it could be judged after mastering the rules of morphological characteristics.(2)In addition to the samples made by the print characters with dispersed ink powder and atom stamp-pad ink,the chronological judgement could be made for other samples with sequencing of stamping and printing within 300 days by polarized optical microscope,and the experimental results are stable.(3)Compared with ordinary microscope,polarized optical microscope was more effective when the pigment material was inkpad and stamp pad ink;compared with fluorescence microscope,polarized optical microscope was more intuitive when the type of laser printed characters is ink powder with porous and dispersed type.