Forensic analysis of crayon via Fourier transform infrared spectophotometry (FTIR) and scanning electron microscopy/energy dispersive spectroscopy (SEM-EDS).

摘要

In this study, the use of SEM/EDS were explored to differentiate between different brands of crayons. Fourteen different brands of crayons were obtained by the author from local stores. One blue crayon and one red crayon from each brand were visually color matched and selected for analysis. Examination of color alone was found to be a poor discriminator for crayon analysis as the apparent color was highly dependent on sample thickness. Each of the fourteen different brands of crayon could be differentiated via either their FTIR spectra or elemental analysis of extenders via SEM/EDS. Elements quantified and compared via EDS analysis were silicon, magnesium, aluminum and calcium. It was also found that inorganic extender pigments, present in all the crayons tested, were poorly dispersed in some brands of crayon, resulting in random pockets of extenders throughout the crayon. These pockets were visualized using a backscatter detector coupled with the scanning electron microscope (SEM/BSD) which enhances atomic number contrast. When a person writes with this type of crayon, "bands" of the extender pigment are transferred to the written page and can be visualized by SEM/BSD. The bands of extender pigment can then be compared to test samples produced with the suspect crayon. Since these bands are the result of a random distribution of extender pigment, it is possible under certain circumstances to individualize a portion of handwriting to a single crayon.