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Recommendations include using a FFU test sample at the beginning and end of a series involving the examination of multiple questioned documents, or placing a small FFU test sample adjacent to each questioned document on the platen. The FFU test can be prepared by hand using a similar writing instrument and similar paper. Alternatively, a special device call the 'Gradient®' can be used to produce control indentations that vary in depth in a known manner thereby permitting the examiner to determine not only that the EDD is working but also the degree to which it is sensitive. It is not essential to precisely match the questioned document in terms of paper type or pen type since the objective is to show that the device is functioning properly.
94:
to models like the 'Thickness
Variation Theory' and the 'Surface Variation Theory'. However, it turns out that a detectable 'indentation' is not due to the physical pressure applied to the writing instrument as one might expect. Rather, Seward in 1998 and 1999 proposed an alternative theory explaining the detection capability of an EDD as being due to a surface charge effect created by paper-to-paper friction specifically in the area where a writing instrument is pressed down into the top-most sheet of paper. Seward's model was based upon "charge transport through the Mylar-paper-platen structure" and is appropriately called the 'charge transport model'.
66:
270:
the charging film, thus trapping and fixing the toner in place between the films. Pressure is then carefully applied to the top of the fixing film by hand or with a small roller. The resulting sandwich is referred to simply as a "lift", or EDD lift. Interpretation of the developed indentations is generally done using the lift after removal from the document because this permits the examiner to see the developed indentations on their own without interference from any visible markings on the document.
58:
192:
required to 'develop' any latent indentations on the document. The film should be laid over the document taking care to avoid wrinkles or excessive stretching of the film. Most EDD devices have a roll of bulk film positioned adjacent to the device for ease in application. The charging film will adhere to the platen due to suction applied through the surface of the platen.
188:
and other multipage items can also be examined in some instances but these require additional preparation. Ideally, individual pages should be removed from such items but this is not always possible. As an alternative, a sheet of conductive material (e.g., aluminum foil) can be used to contact the conductive surface.
133:
Assess adequacy of material for examination: an EDD works best when used on a single sheet of clean, smooth paper (that is, paper without wrinkles, creases or stains). The presence of any of these factors may preclude effective examination or, at the minimum, mean that the results will be limited.
85:
might match information present on another such document. In some situations this would be an entirely innocent finding; however, if the two businesses are supposed to be operating independent of one another, then the finding could be significant. Decipherable indentations may also provide valuable
215:
Aerosol spray method: Some EDDs provide the ability to spray toner over the surface of the charging film. In these systems a protective shell or chamber is fitted that covers the entire platen. At one end there is a nozzle connected to a reservoir of toner. The examiner then manually activates a
175:
Placement on platen: the goal is to place the questioned document flat on the platen surface with few wrinkles or distortions (ideally, none). The document should not extend beyond the platen edges and enough room should be present around the document to allow the charging film (see below) to seal
93:
The electro-physical basis whereby an EDD actually works is complex. The original theory suggested that the paper sandwiched between the grounded platen and the mylar charging film acted as a type of capacitor with the change in capacitance being due to differing compression of the paper. This led
617:
Experiments have been performed which show conclusively that, under certain conditions, 'impressions' of writing can be detected by ESDA (ElectroStatic
Detection Apparatus) on paper which has been placed in contact with the reverse of paper bearing writing which has significantly embossed the back.
211:
Cascade method: Some EDDs have a platen that is hinged on one edge to permit it to be tilted. A mixture of toner and small carrier beads (made of glass or similar non-conductive material) is then poured over the surface of the document from one side to the other. The beads, and excess toner, are
163:
Humidification: an EDD works best when the relative humidity is less than 60%. Some studies have also suggested that absolute humidity is important. To help ensure proper humidification, most manufacturers provide a 'humidification chamber' that can be used to prepare a document for examination.
97:
Subsequent testing demonstrated that the charge transport model, while not perfect, is sound. This testing also clarified that areas of indentation are less negatively charged than surrounding areas. It is this relative difference in potential that causes the toner to be attracted to the areas of
269:
Adhesive lift: in this method, a sheet of fixing film is used to preserve the developed indentations. The fixing film is usually a relatively rigid sheet of self-adhesive, transparent polymer film. It is applied by removing the backing material and carefully laying the fixing film directly onto
187:
sheet. However, if there are concerns about biological or chemical contamination, due to the condition of the questioned document, it is possible to use a second sheet of clean paper, e.g. copier paper, known to be free of indentations as a barrier between the platen and questioned document. Books
112:
Additionally, indentations can sometimes not develop very well even though they are clearly visible. This may occur, for example, with very heavy or deep impressions or with impressions in glossy heavy-weight paper such as that used for brochures. In such situations, it is possible to use digital
252:
If the FFU test was positive and no indentations are developed in the area of the questioned document, then the assessment will be that no detectable indentations have been developed. It is important to note that this does not mean the questioned document was never in contact with other items of
207:
Application of toner to develop indentations. The EDD is able to visualize indentations because the surface is differentially charged depending upon whether or not an indentation is present. The negatively charged toner particles are attracted to areas where there are indentations in the paper
203:
charged. To achieve this most EDDs use a shielded (grounded) hand-held unit containing a high-tension corona wire which is usually about 7kV. It is turned on and literally waved over the entire surface of platen for several seconds criss-crossing the platen area. The objective is to produce an
794:
However, we have further shown that relative humidity alone is not the primary determinant of the quality of ESDA results; at high levels of relative humidity and low temperatures there is a significant reduction in the quality of results and at very low relative humidity and high temperatures
822:
This poster describes a device capable of producing control impressions in paper. Each impression varies in depth from 0.000" to 0.002". These controls or test strips not only verify when equipment and experimental conditions are satisfactory but they can also be used to quantify EDD results,
191:
Covering with charging film: As noted above, the charging film should cover the document completely and contact the platen all the way around the document. The charging film serves two purposes: it protects the document from subsequent toner application and it takes the electrostatic charge
32:
in paper that may otherwise go unnoticed. It is a non-destructive technique (will not damage the evidence in question), allowing further tests to be carried out. It is a sensitive technique capable of detecting indentations on pages several layers below the top sheet and many years after the
167:
Fitness-for-use (FFU) test; AKA, control sample: since an EDD may fail to detect indentations when they are actually present (for a variety of reasons), it is important to check on the equipment's performance using a control sample (commonly called a FFU test) known to have indentations.
208:
surface. Once an electrostatic charge has been applied to the charging film, the latent indentations can be developed. This is done using a powder toner very much like toner found in any electrophotographic printing device. There are various methods used for this purpose.
216:
pump that sprays toner into the chamber creating a cloud of fine toner that settles down onto the surface of the charging film. Ideally the cloud is randomly distributed but often this method produces a relatively distinctive pattern of toner on the film.
407:
The sourcing/matching of indentations must be interpreted in the context of the investigative scenario. That is, indentations and source writing that 'match' indicate only that pieces of paper were in physical juxtaposition at the time the writing
137:
Examination using side (oblique) lighting: as a general rule, all items should be examined using side lighting. This is important because visual examination may detect deep indentations even though the EDD may fail to develop those indentations
204:
evenly distributed electrostatic charge in the air above the surface of the charging film. After passing the unit over the platen, the examiner waits for a few minutes until the charge has been passed to the surface of the charging film.
121:
Despite the complexity of the underlying theoretical mechanism, the practical use of an EDD is straightforward. Most devices are similar in their operation. The following are the key steps in using an EDD to visualize indentations:
273:
Photography/scanning: the results may also be captured using a camera, either directly from the charging film or from the lift after removal from the document. Scanning is also an option but only when using the lift
134:
Heavy-weight, coated or treated papers often produce poor results. The purported age of the document is not generally a factor of concern. Latent indentations have been developed on documents older than fifty years.
906:
Craig, C.L.; Hornsby, B.M.; Riles, M. (July 2006). "Evaluation and
Comparison of the Electrostatic Dust Print Lifter and the Electrostatic Detection Apparatus on the Development of Footwear Impressions on Paper".
226:
Toner pad method: Similar to the brush method described above but uses a special pad with a built-in toner reservoir. The toner pad is placed on the surface of the charging film and moved across the surface by
436:
Foster and
Morantz attributed the ESDA image of indented writing to a change in capacitance of the Mylar-paper-platen structure (2). This change in capacitance was theoretically due to the compression of the
1020:
53:
When writing is fashioned on a sheet of paper resting upon other pages, the indentations or impressions produced are transferred to those below. These transferred impressions can be detected using an EDD.
265:
Preservation of results. It is important to record and/or preserve the results of a test, especially if the test is positive (i.e., indentations were developed). This can be done in at least two ways.
44:
that were appealed. The allegations of tampering with evidence and witness statements led to the unit being disbanded, and over 60 convictions being quashed, many of the appeals relying on EDD evidence.
40:, as it was possible to demonstrate that witness statements had been altered or signed as blank pages in reverse order to the main notes. This was central in a number of cases investigated at the
81:
letter, may exist which can be determined to be the source of indentations detected on another piece of paper (e.g., an offender's notepad). Alternatively, indentations detected on a business
998:
141:
Documents that have been subjected to high levels of humidity will not generally retain indentations. As a result, other forensic examinations involving the wetting of a document, such as
235:
FFU test results: since the questioned document may or may not have indentations, the correct method to assess the functionality of the EDD is through inspection of the FFU test sample.
1056:
806:
The Foster + Freeman ESDA user manual states "Over-humidification may have the same effect as wetting the document with a liquid. The ESDA image may be degraded or obliterated."
223:. This is a manual process that is quite tedious and requires meticulous control of the brush. But the method works well for selective development of subtle indentations.
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acceptable results can be obtained. These data strongly suggest that it is the absolute humidity of the atmosphere used that determines the quality of the ESDA results.
69:
Example ESDA result developed on a sheet of paper positioned beneath the written note at the time of writing (shown above), and developed using the bead cascade method
108:
indirect secondary 'impressions' may appear that are caused by lateral relative motion between two sheets of paper when the source sheet bears significant embossing.
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Note that the presence of indentations in the document area is prima facie evidence that detectable indentations exist such that the FFU test is redundant.
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may bear impressions of writing that relate to some mundane activity of the offender which could ultimately lead an investigator to a particular suspect.
546:
Yaraskavitch, Luke; Graydon, Matthew; Tanaka, Tobin; Ng, Lay-Keow (2008), "Controlled electrostatic methodology for imaging indentations in documents",
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374:
284:, fiber disturbance on the paper surface (e.g. relating to mechanical erasure of information), or the presence of footwear impressions on paper.
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captured on the lower edge of the device to be reused. This process can be repeated several times in order to develop all areas of the document.
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In contrast with Seward's findings, a period of charge decay before image development is not required when operating in this optimal regime.
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776:
Pearse, M.L.; J.S. Brennan (2 December 1996). "Importance of absolute humidity in the operation of the electrostatic detection apparatus".
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Strach, Steven J.; McCormack, Graeme M.; Radley, Robert W.; Westwood, Paul D. (1995), "Secondary impressions of writing detected by ESDA",
744:
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A single strand of wire through which a high voltage, usually 7kV, electrical charge is passed similar to a corona wire used in some
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Many systems use a sintered brass plate for the platen but any porous and conductive surface would, in theory, work for this purpose
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interest. The absence of detectable indentations may be due to one or more limitations causing the indentations to not be detected.
41:
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A detailed presentation followed with experiments, of how the ESDA device is useful in
Forensic Handwriting Examination (in Greek).
950:
Foster, D.J.; Morantz, D.J. (1979), "An
Electrostatic Imaging Technique for the Detection of Indented Impressions in Documents",
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Tanaka, TA (2000), "An
Evaluation of the Methods for Optimal Development of Indented Writing as Suggested by the Seward Method",
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25:
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Assessment of results. After the development process is complete the examiner must assess the results of the test process.
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optimize experimental conditions or develop protocols that optimize results and ensure critical evidence is not overlooked.
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Brush method: With some EDDs the toner is applied using a magnetic brush such as would be used for development of latent
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It is important to note that over-humidification is also possible so care must be taken to not actually wet the document.
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The platen size varies by device. As an example, the platen on the Foster + Freeman ESDA is approximately 24cm x 42 cm
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Such indirect 'secondary' impressions are caused by some degree of lateral relative motion of the two sheets of paper.
328:
Lightning Powder
Company, Inc. manufactures two units: the Electrostatic Vacuum Box and Vacu-Box™ for Indented Writing
65:
520:
Seward, GH (1999), "Practical
Implications of Charge Transport Model for Electrostatic Detection Apparatus (ESDA)",
418:
Seward, GH (1999), "Practical
Implications of Charge Transport Model for Electrostatic Detection Apparatus (ESDA)",
478:
Seward, GH (1998), "Model for electrostatic imaging of forensic evidence via discharge through Mylar-paper path",
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pparatus) which is the original such device developed in 1978. It was designed to meet the requirements of the
675:
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If indentations are developed from the FFU test sample, the EDD can be considered as functioning correctly.
323:
754:. Centre of Forensic Sciences, Ministry of Community Safety and Correctional Services, Ontario, Canada
449:
Wanxiang, L.; Xiaoling, C. (1988), "A study of the principle of the electrostatic imaging technique",
382:
36:
EDD equipment and investigative techniques were central to overturning a number of convictions in the
487:
716:
Horan, G.J.; Horan, J.J. (November 1988). "How long after writing can an ESDA image be developed?".
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Seward's model also helps to explain two unusual phenomena sometimes observed when using an EDD:
1036:
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information even when a second document is not present or cannot be located. For example, an
676:"ANSI/ASB Standard 044, First Edition Standard for Examination of Documents for Indentations"
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and is still in production today in two different forms: the ESDA® and ESDA-Lite® (portable)
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Aside from visualizing indentations, the method can be used to detect the presence of fresh
105:'pure' indentations caused by impact printing, for example, may not produce good EDD results
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Fingerprinting using ninhydrin and other solvents inhibits the development of indentations
183:
Type of document: as noted above, an EDD works well with a single sheet of paper up to a
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Mock-up of a handprinted robbery note written on the top-most sheet of a pile of papers
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The carrier material and toner composition is carefully designed based upon their
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Purdy, Dan (2005). "Gradient® - a device for producing uniform EDD test strips".
281:
220:
142:
29:
375:"ESDA and the Analysis of Contested Contemporaneous Notes of Police Interviews"
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An EDD is a highly specialized device and there are only a few manufacturers:
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If no indentations developed from the FFU test sample, the EDD is not working.
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Strach, Steven J. (Sep 2007), "Writing impressions revealed by scanners",
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evice) but their website no longer lists this device in their product line
1023:. Lightning Powder Company Inc. Archived from the original on 21 Oct 2006
82:
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Some manufacturers refer to this as a toner application device, or TAD.
820:. Montreal, Quebec: American Society of Questioned Document Examiners.
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solution, should not be done until after examination for indentations.
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scanning and image-processing to document such writing impressions.
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Charging of surface: the top surface of the charging film must be
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Some manufacturers have built in a 'catch tray' for this purpose.
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devices. Some manufacturers refer to this as a 'corona wand'.
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Kinderprint (now CSI Forensic Supply) used to manufacture the
752:
Investigators & Submitters, Technical Information Sheets
706:
Foster + Freeman ESDA-2 User Manual 14-06, July 2008 (UK/US)
98:
indentation, rather than other areas on the mylar surface.
24:, is a specialized piece of equipment commonly used in
834:
Some manufacturers refer to this as an "imaging film"
73:
In some situations, a questioned document such as a
296:Foster + Freeman Ltd manufactures and markets the
1113:CSI Forensic Supply (formerly Kinderprint) site
818:Proceedings of the 2005 ASQDE Annual Conference
1059:. Lightning Powder Company Inc. Archived from
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1123:A more detailed description of the process
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324:Projectina manufactures the Docustat DS-220
745:"Examination for Indentations Information"
632:Forensic Science, Medicine, and Pathology
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471:
1057:"Redwop: Vacu-Box™ for Indented Writing"
586:Proceedings of 58th Annual Meeting ASQDE
952:Journal of the Forensic Science Society
878:properties to ensure proper deposition.
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1118:Projectina CH Docustat 220 information
1108:Foster + Freeman Ltd. ESDA information
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381:(1). Routledge: 71–89. Archived from
7:
1021:"Redwop: Electrostatic Vacuum Box"
14:
743:MacVicar, R. (December 6, 2007).
396:West Midlands Serious Crime Squad
42:West Midlands Serious Crime Squad
921:10.1111/j.1556-4029.2006.00173.x
1153:Questioned document examination
560:10.1016/j.forsciint.2007.11.004
26:questioned document examination
778:Forensic Science International
718:Forensic Science International
601:Forensic Science International
548:Forensic Science International
18:electrostatic detection device
1:
790:10.1016/s0379-0738(96)02026-9
463:10.1016/s0015-7368(88)72841-8
398:for full details of the cases
964:10.1016/0379-0738(79)90262-7
909:Journal of Forensic Sciences
730:10.1016/0379-0738(88)90084-9
613:10.1016/0379-0738(95)01761-7
522:Journal of Forensic Sciences
451:Journal of Forensic Sciences
420:Journal of Forensic Sciences
176:against the platen surface.
33:indentations were created.
30:indentations or impressions
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480:Journal of Applied Physics
1041:: CS1 maint: unfit URL (
644:10.1007/s12024-007-0015-4
1001:. Foster + Freeman Ltd
979:. Foster + Freeman Ltd
126:Evaluation of material
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1085:. CSI Forensic Supply
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379:Forensic Linguistics
145:development using a
1148:Forensic techniques
863:electrophotographic
492:1998JAP....83.1450S
373:Davis, Tom (1994).
1143:Forensic equipment
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