Frequently, those instructing merely ask whether, for instance, a signature on a document is genuine. However, a signature may well have been written by the individual said to have produced the same but the remainder of the document itself may not be genuine. Consideration of other factors such as whether text has been added to a document, whether there has been alteration to a text, whether a document has had pages substituted, whether the document has been signed in blank, back-dated etc. should always be considered in forensic casework.
To this end, the laboratory is equipped with an extensive range of equipment to assist in such matters.
One of the most valuable tools of the questioned document examiner is microscopy which supplements any visual examination of a document or preliminary examination using hand magnifiers etc. A stereo binocular microscope can show both low and high magnification of images which is essential in the forensic examination of the fine detail of signatures, handwriting and documents generally.
Infrared reflectance and luminescence equipment is available (together with visual luminescence facilities) to distinguish between inks, identify the presence of foreign substances (glues etc) on documents etc. Instant video printout systems (similar to photographs) are also incorporated into the system (black and white and colour), as is a VCR recorder to capture images for later use or to record changing images.
The above equipment is supplemented with the use of a Polylight, a powerful tuneable light source that can be used to promote both visual and infrared luminescence in order to differentiate between inks.
The above techniques are routinely used and are wholly non-destructive.
Thin Layer Chromatography
However, on very rare occasions, chemical analysis of inks utilising thin layer chromatography is necessary and can be undertaken but requires the removal of a short section of an ink stroke for analysis, i.e. this is a "destructive" test. This procedure is generally used as a last resort after all other examinations by all parties' experts and then only with the written permission of the owner of the document in question or on instruction by the Court.
The ADV2 instrument facilitates multiple integration of images, enhancing contrast of images, superimposition and nictitation (flicker) comparison of similar images, creation of mirror images etc. Digital photography and computer capture of images is also extensively used.
This technique is applied to virtually all questioned documents submitted to the laboratory.
This equipment reveals writing impressions on documents that have been caused by one document having been written upon whilst physically resting on top of the document under examination. The writing process consequently imparts impressions of the writing onto the document below leaving visible indented writing impressions in the underlying paper surface or electrostatic writing impressions invisible to the naked eye which can be highlighted with the ESDA technique.
The technique can reveal valuable information relating to the history of documents, the association of documents one with another during preparation, the origin of documents, the presence of tracing guidelines etc and is considered to be an extremely valuable tool in any forensic investigation.
High and low intensity ultraviolet equipment
This is of great value in examining and differentiating between papers, glues, stains and for revealing chemical or physical erasure sites, etc.
A variety of conventional cameras, video printers (black/white and colour) and computer scanning facilities are available to capture evidence and if necessary prepare illustrations for court presentation.
A variety of measuring devices, measuring grids, micrometers, graticules, typewriting grids etc are available where the precision of absolute measurement is imperative.
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