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Thermic Transformations of Writing Materials

NCJ Number
Problems of Forensic Sciences Volume: 53 Dated: 2003 Pages: 51-59
Miroslaw Owoc
Date Published
9 pages
Since computer laser printers and photocopiers are increasingly used in document forgery--either in creating a document with the use of a signature placed previously when the paper was blank or in alterations in the text of a previously made document--this article describes a method that unequivocally determines the chronology of inscriptions when one inscription involves the thermic process used in laser printing.
The described procedures rely on the well-known rule that the melting temperatures of mixtures are lower than the melting temperatures of the pure components of the mixture. This rule proved correct in cases where the immediate contact of micrometer particles of a laser-printer toner contacted the surface of a previously existing line (e.g., ballpoint ink). The melted agglomerates of toner particles underwent a change at those places where it contacted previously applied substances used in inscriptions on the document. This was due to changes in melting temperature when the different substances in the toner and the previous inscription mixed at crossing points. The predicted effects were observed for the crossing points with ballpoint inks, colored pencils, and crayons. The article concludes that the disturbances in the "normal" melting of a toner's agglomerates was due not only to the composition of the surface below the toner but also to the depth of the relief in the document surface produced by a writing tool. This caused a narrowing of the breadth of the line of a photocopy imprint at the spot of the crossing lines. These effects could be clearly observed under the optical microscope with the magnification of 30 to 60 times. The article advises taking photographs of these effects in the scanning electron microscope. Pictures of the effects provided in the article used the magnification of 75 and 150 times (specimens sprayed with gold). 4 figures and 2 references