Wherever question over the authenticity of any document is raised, the questioned document examiners are called upon. Questioned document is basically a document having authenticity under question which is subjected to a forensic document examination. The primary purpose of examining the disputed documents is to give opinion upon the questions that are raised upon the authenticity of the document using scientific principles and techniques. Questioned documents could involve any type of document for an instance a property will, a suicide note, a blank sheet possessing indentations, bank cheques and many more. The examination of documents includes detecting alterations and obliterations, analysis of paper, detection and examination of forgery, origin, determining authenticity, and others.
This blog summarizes various techniques utilized in forensic examination of inks as well as the importance of ink analysis so far in the field of investigation.
The forensic document examiner plays a crucial role of uncovering the minute details in the document sample such as in signature or in handwriting. These are the details that cannot be detected or uncovered by an untrained person.
The forensic analysis of ink is a frequent requirement in casework in order to identify whether the inks on a document or documents are same or different. Hence, the document examiners are often called upon to identify the ink involved and to determine the actual source of the ink on a document. It’s a crucial part of forensic document examination since it is used in both handwritten and printed documents.
The importance of ink analysis has been noted in case of obliterations for differentiating the ink on basis of its chemical composition; further, the source and also the age of ink which ultimately gives the approximate age of the document providing leads and clues in the investigation process. There are different types of inks available which are used in different pens such as ball pen ink composing of dyes and organic solvents, gel pen, roller ball pen which uses gel-based inks, fiber or porous tip pen, fountain pens that uses water-based inks etc.
Integrity of the sample having evidential importance is of fundamental value in forensic examination. Hence, in order to maintain the integrity of documents, the non- destructive techniques are always preferred over the destructive ones.
Preliminary examination of ink is performed prior to the chemical and instrumental analysis. This includes examination of ink by the use of microscopes and optical sources without detaching the inked portion from the document.
The stereomicroscope is used to determine the type of ink, its color or to determine additional marks generated due to pointed tip, blunt tip, damaged writing tip leading to the identification of a class of writing instrument. This helps in determining the composition of ink used. In optical examination various light sources like UV radiations, IR radiations are used as different inks reflect differently with these light radiations.
We are aware about the fact that the unaided human eye can perceive only a certain range of colors of a particular wavelength in the electromagnetic spectrum. Yet there are other ranges also present such as infra red and ultra violet range. Although these are invisible but can be converted to visible using instrumentation. VSC is that one comprehensive digital system which aids our eyes to perceive these invisible ranges.
Inks are composed of different dyes. These dyes or the colors can appear similar to our unaided eyes. For example, two blue colored inks are difficult to be differentiated by visual observation as the color is same but the colors could behave differently when perceived under UV or IR range. It’s this behavior that lets the examiner differentiate it. The specialized filters of light and the photographic films allow uncovering the minute details of the document sample. These aids show peculiar properties such as luminescence, transparency, etc. depending upon the chemical properties. Thus, the VSC is one of the reliable instruments used for the questioned document examination.
Techniques incorporating chemical analysis of the ink present on the document fall under destructive category since for sample analysis the portion of the document containing ink is cut and thus the sample is destructed.
Various chromatographic techniques such as TLC, GLC, and HPLC are utilized for the qualitative ink analysis in order to separate the components of ink thereby determining the composition. Most commonly used technique is the TLC (Thin Layer Chromatography) which incorporates the use of chromatographic plate and the alcohol based solvent for the purpose of ink separation.
It is similar to HPLC but uses a small amount of samples. Hence, adopted in cases where the sample is limited. Herein, the capillary is filled with a conductive fluid with a designated pH value. The conductive fluid then serves as the buffer solution in which the sample is separated.
It is used for the characterization of ink. The dyes, additives and solvent present in the ink show different absorption peak in the spectrum which are unique for every substance and compared with the standard peaks for identification purpose.
GC along with MS i.e. mass spectrometer is one of the best techniques used for ink analysis wherein firstly the components are separated by gas chromatography followed by the identification on the basis of mass/charge ratio.
In the examination of questioned documents, the non-destructive techniques are preferred until and unless it is very necessary to adopt the destructive ones in order to reach to a definite conclusion.
“Alteration/Obliteration & Ink Examinations.” Questioned Documents - Norwitch Document Laboratory, www.questioneddocuments.com/alteration-obliteration-ink-examinations/.
“Ink Analysis.” Forensic Examination Services, www.docexam.co.uk/ink-analysis-41.html.
Teresa. “Introducing The Role Of The Handwriting Forensic Document Examiner.” Handwriting Forensics Blog, 9 Sept. 2017, teresadeberry.com/introducing-role-forensic-document-examiner/.
Posted January 16, 2019. “The Role and Importance of a Forensic Examiner.” Marty Pearce, CDE, 16 Jan. 2019, www.martypearce.com/the-role-and-importance-of-a-forensic-examiner/.