Examining the sequence of intersecting seal and laser printing line is a significant method of determining the authenticity and validity of documents. In this study, five brands of stamp pad inks, three types of inkpads and seven kinds of laser printers were used to make heterogeneous line intersections. Observation method of physical characteristics, scraping technique and fluorescence method was used to determine the sequence of intersecting lines. Distinguishing features were noted between the materials produced in both sequences. As the results obtained from the study were positive, these features might provide a scientific basis for accurately determining the sequence between laser printing line and inkpad (stamp pad ink) seal.
Stamp‐pad ink seals are often placed on important documents, and determining the dating of stamp‐pad ink seal is important to assess the authenticity of a document. In this study, 20 different brands and types of stamp‐pad inks were classified by ultraviolet visible spectrophotometer. Six different brands and types of papers were classified by micro‐Fourier transform infrared spectrometer and visual spectral comparator 6000. Three different brands of stamp‐pad inks and two different types of paper were used to make diachronic samples of the seals. A method was employed to date the stamp‐pad seals by comparing absorbance ratios and inks of known age. Curves were created to show the relationship between the absorbance ratio of ink and the age of the seals. The experimental results showed that the absorbance ratio method was applicable for the relative dating of stamp‐pad ink seals in some cases where the seal was placed on the document within 10 weeks.
Determining the sequence of intersection lines is a challenge in forensic document examination. To explore more advanced technology and meet the needs of practical applications, this study proposes a method based on the characteristics of the molten state to examine crossing-line sequences. This state can be considered as a melting state of solid laser toner through a dissolution process. Experimental results demonstrate that the molten state is always visible at intersections when a particular ink is stamped after laser printing; however, the presence of the molten state when the seal is stamped before laser printing largely depends on the time interval between printing and stamping. The degree of error obtained through blind tests indicates that this approach has its limitations; however, a high accuracy, which refers to the ability of an examiner, was achieved with respect to determining the sequence of strokes when using a fluorescence method in conjunction with this method. This further indicated the limitation of a single method and the importance of combining multiple methods for document examinations.
Determining the application sequence of hand‐written pen ink and printer toner lines has attracted significant interest in questioned document examination. This study uses coaxial light to determine line‐crossing sequences, with intersections observed under a VSC600 forensic document workstation and a Leica M205A Stereo‐microscope. Results show that reflected light at intersections and color contrast between intersections and nonintersections was observed when a hand‐written ink line passes over a toner line, while a toner line passing over a written line appeared dull, with no color contrast. The procedure was tested under a range of conditions, such as types of writing pens and laser printers, the writer, and writing pressure, with the latter playing an important role in the evaluation. To validate the results, a 90% detection rate and 98% accuracy rate were achieved from 50 samples of blind testing, which is more effective than optical microscopy.
Two new kinds of writing tools are popular in China's market. One is a self-fading pen, and another is an erasable pen. The ink of the two kinds of writing tools has a remarkable characteristic that it can gradually fade or disappear under heat or be rubbed off. How to reveal the disappeared written lines is a very important question for document examiners. In this article, three series of ink line samples were made with five types of self-fading pens, 18 types of erasable pens, and three types of papers. Temperature, humidity, and lighting are known as influential factors of the process, and the effect of fading was examined. Luminescence, ultraviolet (UV), sidelight, electrostatic indentation development,low temperature, and solution revealing methods are found to be effective methods used to reveal the disappeared written lines. The best operating conditions for each method were obtained from the conducted experiments.
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