ESDA, stands for Electrostatic Detection Apparatus, is a non-destructive technique used for document examination.
Introduction
ESDA stands for Electrostatic Detection Apparatus. The instrument is utilized in the questioned document examination to detect any indentations or impressions that may exist on paper. Foster and Freeman are the manufacturers of ESDA. The technique described is susceptible and can detect indentations on paper. ESDA refers to a device used for detecting electrostatic charges. The electrostatic detection apparatus (ESDA) is a forensic document examination technique routinely employed by examiners. This method enables the detection of imprints on a document, similar to invisible carbon paper, left by items that may have been written on a sheet placed on top of the examined document. In the context of legal cases, its applications include revealing conflicting evidence and uncovering potential forgeries.
Also Read: Instruments Used in Ink Analysis
Working of ESDA
ESDA is a specialized equipment consisting of several components, including an ESDA machine, a thin base for holding the document, a cellophane (plastic film) that is secured onto the document using vacuum technology, an electrostatic charge device, and a toner. The toner used in this device is comparable to the toner used in electro-photographic printing devices.
ESDA utilizes the method of stretching a Mylar film, similar to Clingfilm, over the document under examination. The Mylar film is charged electrostatically using a “wand” that consists of a long, thin stick or rod containing a fine wire charged to 7 kV. In areas where the paper is smooth, the charging tends to be evenly distributed. The electrostatic charge in areas where the fibers of the paper have been disrupted due to contact with other paper, resulting in indentations, is distinct from the surrounding background charge. The process described results in the formation of a latent image. The latent image can be visualized by applying black toner to the surface of the Mylar. The toner adheres to the areas where the electrostatic charge accumulates, specifically in the indentations. The outcome is a visual representation featuring a background with a grey toner shade and darker toner markings in regions with depressed impressions. The image is made permanent through a process called “lift,” which involves placing a clear “sticky-backed plastic” over the toner to create a fixed transparent image.
Examination of Questioned Document
There are three methods for applying toner onto the Mylar film:
- The first method involves cascading tiny glass beads coated with toner over the surface.
- The second method involves puffing an aerosol of toner powder over the surface.
- The third method involves using a device similar to a powder puff to apply the toner.
The presence of the paper between the grounded plate and the Mylar charging film creates a capacitor-like effect. The capacitance is determined by the varying compensation of the paper. The page believed to have indentations is covered with a cellophane material. This material is then pressed firmly against the paper using a vacuum created by pulling air through a porous bronze plate. The purpose of this action is to secure the document and cellophane covering to the plate. The presence of a cellophane covering serves the purpose of safeguarding the original document from potential harm or damage. The document and cellophane undergo a repeated high voltage static charge.
The quality of ESDA lifts is influenced by numerous variables. The factors to consider in analyzing the impressions left on paper include the type of paper, the type of pen or stylus used, the number of sheets of paper between the writing and the sheet holding the impressions, and the humidity at the time of impressions.
Advantages of ESDA
There are two advantages associated with electrostatic detection. ESDA is non-destructive. The protective mylar surface reveals the indentations, which are then sealed by covering the cellophane with pressure-sensitive adhesive plastic. Second, the original document is not damaged at any point throughout the procedure. The Second advantage is that ESDA is so sensitive that it can easily detect and allow for the visualization of indentations up to 7 sheets below the page where the original writing was made that would be impossible to detect with any other technique.
Disadvantages of ESDA
The disadvantage is that it is unsuitable for examining loose paper, such as newspapers, or very glossy materials, such as magazine covers. ESDA impressions will be completely destroyed if the document comes into contact with liquid.
References
- Allen, M. (2015). Foundations of forensic document analysis: theory and practice. New Jersey: John Wiley & Sons.
- Baier, P. E. (1983). ‘Application of Experimental Variables to the Use of the Electrostatic Detection Apparatus’. Journal of Forensic Sciences, 28(4), pp. 901-910.
- Barton, B. (1989). ‘The use of an electrostatic detection apparatus to demonstrate the matching of torn paper edges’. Journal of the Forensic Science Society, 29(1), pp. 35-38.
- Cheng, K., Chao, C., Jeng, B., & Lee, S. (1998). ‘A new method of identifying writing sequence with the laser scanning confocal microscope’. Journal of Forensic Science, 43(2), pp. 348-352.
- Daéid, N., Hayes, k., & Allen, m. (2008). ‘Investigations into factors affecting the cascade developer used in ESDA—A review’. Forensic science international, 181(1-3), pp. 1-9.
- D’Andrea, F., Mazzella, W., Khanmy, A., & Margot, P. (1996). ‘Effects of the Relative Humidity and Temperature on the Efficiency of the ESDA (Electrostatic Detection Apparatus) Process’. International Journal of Forensic Document Examiners, 2(3), pp. 209-213.
- Ellen, D. (2006). Scientific Examination of Documents: Methods and Techniques (thirded.). Boca Raton, USA: Taylor and Francis Group.
- Fatima, F. (2019). ‘Handwriting Analysis from Individual Profiling to Forensic Questioned Document Examination’. International Journal for Electronic Crime Investigation, 3(1), pp. 13.
- Foster, D., & Morantz, D. (1979). ‘An electrostatic imaging technique for the detection of indented impressions in documents’. Forensic Science International, pp. 51-54.
