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Determining Line-Crossing Sequences Between Laser Printing and Writing Pen Using Coaxial Light
Xiang Wu1, Guoliang Ouyang1, Biao Li1
1Department of Document Examination, Criminal Investigation Police University of China, No. 83, Tawan Street, Shenyang, 110854, China.
Journal of Forensic Sciences
|March 24, 2020
Summary
This study reveals how to determine if pen ink or printer toner was applied first. Coaxial light analysis of line intersections accurately distinguishes between ink-over-toner and toner-over-ink sequences in questioned documents.
Area of Science:
- Forensic Science
- Document Examination
Background:
- Determining the sequence of intersecting lines (hand-written ink and printer toner) is crucial in questioned document examination.
- Existing methods may lack accuracy or require specialized equipment.
Purpose of the Study:
- To develop and validate a method using coaxial light for determining the application sequence of hand-written ink and printer toner lines.
- To assess the effectiveness of this method compared to traditional optical microscopy.
Main Methods:
- Utilized coaxial light to examine line intersections under a VSC600 forensic document workstation and a Leica M205A Stereo-microscope.
- Observed reflected light and color contrast at intersections under various conditions (pen types, printer types, writer, writing pressure).
Main Results:
- A distinct "reflected light at intersections" and "color contrast" phenomenon was observed when hand-written ink lines crossed over toner lines.
- Toner lines crossing over ink lines appeared dull with no color contrast.
- Writing pressure was identified as a significant factor in the evaluation.
- Achieved a 90% detection rate and 98% accuracy rate in blind testing (50 samples).
Conclusions:
- The coaxial light method provides a reliable and effective means for determining the sequence of ink and toner lines.
- This technique offers higher accuracy and effectiveness than conventional optical microscopy for this forensic application.
