COHABITATION WITH THE DEAD: Unusual Cases from the Wayne County Medical Examiner’s Office in Detroit

An Approach to Determine the Relative Age of Ink:
A Nondestructive Method Using Hyperspectral Imaging

Nato Locktongbam
Central Forensic Science Laboratory, Directorate of Forensic Science Services, Ministry of Home Affairs, Government of India, Kolkata
Dr. R.N. Khound
Directorate of Forensic Science, Government of Assam, Guwahati
Priyankar Ghosh
Central Forensic Science Laboratory, Directorate of Forensic Science Services, Ministry of Home Affairs, Government of India, Kolkata


The challenges faced by the forensic document examiner are to know whether entries/writings with ink made on certain documents – such as logbooks, registers, OMR sheets, cheques, drafts, promising letter/notes, deeds, wills, prescription notes, and other important documents – are executed during the same period of time, or in different periods of time, and to know whether entries/writings were executed by the same ink. In order to address these challenges, an attempt was made to study the rate of diffusion of inks at different time intervals using hyperspectral imaging. The study was carried out to quantify the amount of ink diffusion using luminosity as a parameter at different intervals of time by preparing a Common Reference Index Value (CRIV) and to assess whether particular writings were made at the same period of time. This study reveals that there are noticeable differences in the rates of diffusion of the same classes of inks, depending on time interval. This new approach can determine the relative age of the ink, in a nondestructive manner, from any two writings created at different periods of time with the same class of ink.

Key Words: age of inks, hyperspectral imaging, relative aging, CRIV, forensic document examination

Originally published in The Forensic Examiner - November, 2015

One of the challenges faced by the forensic document examiner is determining the age of a document/ink in order to ascertain whether entries or writings – such as those in logbooks, registers, OMR sheets, deeds, cheques, drafts, and other important documents – were executed in the same period or in different periods of time.  Many attempts have been made to determine the age of ink in the last 30 years.  Different techniques have been used, based on the study of chemical and physical properties of various types of inks.  Not all published methods are reliable, however, and some have been heavily criticized (Hofer, 2004).  This is because the concepts of absolute and relative aging are not clearly understood.  No specific data bank regarding the chemical compositions and dye components for the various ink types is available.   Moreover, there are many factors affecting the rate of aging, and almost all techniques used to determine age are destructive in nature.

Ball pen inks are made up of colorants (dyes and pigments) and a carrier (vehicle).  The carrier contains most of the substances that age or change with time.  Two important aspects of these components are the ballpoint ink solvents used to dissolve or disperse the colorants, and the resins used to thicken the inks.  The solvents evaporate with time, and the resins harden or set (by oxidation) with time.  Each of these two aging processes causes measurable changes in several aging properties.  More than one method is often used to measure the changes of a given property; each method is associated with an aging parameter.  The two more commonly studied ink aging properties are: 1) how well an ink extracts into a weak solvent, and 2) how much solvent remains in the ink.  For fresh inks, both aging processes mentioned above (solvent evaporation and resin setting) contribute to each of these two properties.  For older inks, the second aging process (setting of resins) predominates.  Some solvents, like oleic acid, do not easily evaporate, but oxidize with age (Cantu, A.A. 1996).

Unfortunately, no specific research is available regarding the aging of gel pen ink, although there are reports on the chemical composition of gel pen ink.  As gel pens are now becoming popular, studies regarding the aging of their ink will likely emerge, and enter into the criminal justice system.

Often, we come across the terms “static/absolute” or “dynamic/relative” in regard to the aging process.  With absolute aging, analytical ages lead to the determination of a time frame, in which a questioned entry must have been produced.  With relative aging, samples of two or more questioned entries (that may be on different sheets or on the same sheet) are analyzed and compared to determine which sample is older or younger than the others (Hofer, 2004).

The objective of this work is to define and corroborate a method of analysis for questioned documents pertaining to the relative aging of writings.

A validated and accepted technique, called hyperspectral imaging (HSI), is becoming a choice of technology for questioned document analysis.  The analysis is nondestructive and requires little or no sample preparation, which reduces the chances of possible contamination, as well as time.  HSI is a standard digital imaging technique with common spectroscopic methods, such as Near-IR, visible and fluorescence imaging that provides increased sensitivity and discrimination capabilities over traditional imaging and detection methods.  HSI uses reflected, transmitted, or emitted light from each point in the sample image to create a spectral-based contrast within the image (ChemImage, 2011).

Examination of ink using hyperspectral comparator (HSC) is a non-destructive process and has repeatable methods.  With the application of this latest technology, the present work, with its innovative approach, will be able to answer:

  1. Questions regarding the relative age of the ink irrespective of data bank concept
  2. Questions regarding whether the entries/writings were executed during the same period of time
  3. Questions regarding the entries/writings being executed during different periods of time
  4. Questions regarding the entries/writings being executed by the same, or different, ink
  5. Questions regarding any part of the entries/writings being subsequently added
  6. Questions regarding any part of the entries/writings being artificially aged
  7. Questions regarding the determination of the sequence of stroke
  8. Questions regarding the determination of the path of aging due to oxidation                     

Hyperspectral Imaging in Forensic Document Examination

Magdalena, Jaun, Gongora, Itxaso, and Rosa (2010) reviewed the different analytical methods that had been used in the field of forensics in dating inks from different modern writing instruments.  The reported works had been classified according to the writing instrument studied and the ink component analyzed in relation to aging.  The study, done chronologically, shows the progress made in recent decades in the field of ink dating.  Halder and Garain (2010) reported on the color feature approach to determining ink age in printed documents.  They made use of the image processing and pattern recognition principle for determining ink age in printed documents.

Marvin et al. (2008) worked on the quantitative hyperspectral reflectance imaging for a user-defined region of interest using wavelength ranging from 365 to 1100 nm to study the degradation effects of historical documents.

E’lyn (2001), in her overview of the basic techniques and technology of questioned document examination, revealed that two new methods of determining the relative age of ball point inks had come to the forefront in forensic document examination.  The new method for analyzing the drying time of ink was through chemical analysis.  Unfortunately, this was a destructive process.  It is now possible to identify the age of the ink to within a six–month period.

Studies regarding the aging and dating of ball point inks, using different techniques and approaches, were carried out by R. Hofer (2004); Jurgen, Hans, and Anton (2008); Andrasko (2002); Lociciro, Dujourdy, Mazzella, and Lock (2004); Celine, Dieter, Cesar, and Bernhard (2006).  All these works, however, were destructive in nature except the techniques used by R. Hofer (2004), who applied ESDA as a nondestructive approach to analysis.

Studies on the degradation of blue gel pen dyes by ion-pairing high-performance liquid chromatography and electrospray tandem mass spectrometry were reported by Liu YZ, Yu J, Xie MX, Jiang GY, and Gao Y (2006).  The identification and dating of the fountain pen ink entries on documents by ion-pairing high-performance liquid chromatography was reported by Wang XF, Yu J, Xie MX, Yao YT, and Han J (2008).

Brauns and Dyer (2006) presented the details, design, and performance characteristics of a new hyperspectral visible imaging technique in their paper, “Fourier Transform Hyperspectral Visible Imaging and the Nondestructive Analysis of potentially Fraudulent Documents”.

Techniques and applications of reflectance spectrophotometry by Forinst – Forensic Instruments (2011) and Hyperspectral Image by Research and Market (2011) – grab headlines in the field of forensic document examination, as these techniques are nondestructive and repeatable.  R. Padoan, Steemers, Klein, Aalderrink, and Bruin (2008) reported in their paper, “Quantitative Hyperspectral Imaging of Historical Documents: Technique and Applications”, that due to an increase in spectral resolution, hyperspectral imager proved to be very useful in detecting differences in writings and enhancing visibility of faint features, such as palimpsest.  A similar work on hyperspectral imaging as a nondestructive way of analyzing palimpsest was reported by Konstantinos & Balas (2009).

Brauns, et al. (2006), in their paper, presented the design and performance characteristics of hyperspectral visible imaging technique.  Rather than using optical filters or dispersing elements, this design implements fourier transform spectroscopy to achieve spectral discrimination.  This new technology is nondestructive in nature and can authenticate written and printed documents.

Jeffrey, Beckstead, and Arjun (2011) in their publication regarding United States patent application, claimed that the use of hyperspectral imaging provides very high spectral resolution on the order of 5nm, which allows for the differentiation of image components with subtle differences.  A spectral tuning resolution of 1nm may be used.

John Ferguson (2011) commented on the application of hyperspectral imaging in different areas, such as industry and agriculture, health care and life sciences, and most recently, in forensic sciences like counterfeit detection, print and ink analysis, document and currency verification, and crime scene investigation, etc.

ChemImage (2011) published a progress report on hyperspectral imaging to discriminating black ball point inks and pointed out that hyperspectral imaging is taking document examination to the next level by increasing the power of discrimination available for ink differentiation with the nature and extent of its technological advancement.

Aims and Objective

Time is the decisive factor for the determination of the age of the ink.  Aging process, apart from its inherent complexity, depends on many factors, such as storage condition and the chemical composition of the ink.  The task is made even more complex by the diversity and rapid evolution of the ink market, which strongly depends on the availability, price, and quality control of the components involved.  As such, the resources that would be required to determine all aging processes of all types of ink under all possible conditions simply do not exist.  As a result, the aim of this work is to study the relative aging of two types of the most common inks, i.e. ball pen ink and gel pen ink, available commercially and regularly, using hyperspectral imaging.  The objective of this work is to define and validate a proper method of analysis for questioned documents pertaining to relative aging of the writings through non-destructive hyperspectral comparator.

It is now possible to identify the age of the ink to within a six–month period (E’lyn Brayn, 2001) and 3-4 months (Maciej and Bogusz, 2008), depending on the nature of examination methods.  The present research also aims to minimize the period of aging less than six months from the samples under similar conditions.

Material and Methods

Preparation of Sample

Samples were prepared (ENFSI-Standing Committee for Quality and Competence, 2007).   Systematic sampling was carried out from the writings made on the A4 sheet paper (J.K Copier) at different periods of time with the minimum interval of fifteen days onwards, i.e. June 14th, 2007 to August 2012, for five times using two different pens: A_ Cello Pentek ballpoint pen (Figure 1) and B_ Achiever Dye stuff add gel pen (Figure 2).  These were kept together in the same room temperature.

Hyperspectral comparator

The most significant feature of VSC6000/HS (Foster Freeman, 2011) was the inclusion of a hyper-spectral imaging module designed to complement the system of existing analysis methods by producing superior ink discrimination.  Hyperspectral imaging had been a relatively new technique in the field of questioned document examination and had previously been considered to be an incredibly high-cost method of analysis.  Now integrated in the VSC6000/HS system, HSI sensors collect and process information from across the electromagnetic spectrum and combine results into a 3-dimensional, multi-layered image cube.  The image that makes up the cube can then be scanned manually in real time for further processing and examination.  It is equipped with a high-resolution color camera and zoom lens, a range of viewing filters, and multiple illumination sources from UV to visible to IR wavelengths.  Instrument functions were selected and controlled through a simple graphical user interface, and the Windows Vista operating system includes casework management and image archiving facilities.  An integral micro-spectrometer allows measurement of reflectance, transmission, and fluorescent and luminosity features (Figure 3) and (Figure 4).


In order to avoid any false positive results during the quantification process of the spectra of the writings with respect to luminosity (parameter for quantification), an approach was made by plotting a minimum of 10 different points at random from the writings of the ink area and calculating their average value.  The value thus obtained is considered the quantified value of the corresponding writings (Figure 5).

Preparation of CRIV

The average value of the corresponding writings (luminosity value) obtained from each of the writings from different periods of time were graphically plotted as Luminosity Value against Time/Days (Figure 6).


If compound A in the ink is transformed to compound B at a known rate once the ink has been deposited on a writing surface and exposed to the air, then a simple quantification of the ratio of A to B can be measured using standard nondestructive analytical techniques, including spectrometry (Frey, Thomas, Lieberman, & Isaiah, 1997).

Ink once exposed to the atmosphere on any substrate (irrespective of type and brand) immediately starts degrading due to the chemical reaction oxidation, and this is the phenomenon known as aging.

The greater the rate of oxidation, the greater the rate of diffusion.  The greater the rate of diffusion, the greater the rate of aging.  Depending on the rate of oxidation, the amount of absorption/reflectance spectra of two writings at two intervals of time will vary.

Equipment sensitive to quantify the rate of changes in the composition of the ink in a non-destructive process.

The elapsed time is then determined by preparing a Common Reference Index Value (CRIV).  The CRIV generated are the ratios that plot the amount of luminosity versus time.

As long as ink is stored inside a pen cartridge, dye components are preserved from degradation and, as a consequence, the vehicle-to-dye ratio is stable (Grim, Siegel, and Allison, 2002).


Combating such fraudulent activities is difficult, because the signatures or writings are authentic to the author, and this information in itself offers no proof as to when the writings were actually made.  Other problems that complicate the determination of this type of fraud are that no reliable and cost-effective technique has been available to accurately identify the age of a deposited ink.  Therefore, there has been no quick and reliable way to determine whether a person signed or wrote a document at the particular date, or that the dates indicated on the document are genuine or not.

What is therefore needed is to develop a method that will make it possible to not only give information about the age of an ink writing, but also to distinguish the relative ages of sequential ink writings entered on a document or series of documents over time.  What can also be proposed is one or more known chemicals adding to an ink that has known and predictable time variable characteristics, in order to cause the ink to change with time after its deposit on a writing surface.



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Figure 1
Figure 1: Sampling of Cello Pentek ballpoint pen inks at different periods of time

Figure 2
Figure 2: Sampling of achiever dye stuff add gel pen inks at different periods of time

Figure 3
Figure 3: Showing the luminosity value of an ink at point (+2)

Figure 4
Figure 4: Showing different luminosity from an ink with the same chemical composition but written at different intervals of time

Figure 5
Figure 5: Showing quantification of the 10 different points from a single writing of the ink area and its mean value

Figure 6
Figure 6: Showing preparation of Common Reference Index Value

About the Authors

Locktongbam Nato Singh

Born on second February1968, Locktongbam Nato Singh was brought up in Imphal, the capital city of Manipur, state of the country India.  Graduating from Manipur University in life sciences in the year 1989, Singh did completed post-graduate studies from Madras University in forensic sciences with specialization in three major disciplines (Questioned Documents, Serology and Genetics, and Biochemistry) in the year 1992. Singh worked as a forensic scientist in the Regional Institute of Medical Sciences, Imphal, Manipur since August 1992, and was later commissioned as Assistant Government Examiner of Questioned Documents by Union Public Service Commission, under Directorate of Forensic Science Services, Ministry of Home Affairs, Government of India in the year 1998. At present, Sing is posted in the Central Forensic Science Laboratory, Kolkata and examines case exhibits as well as tendered evidences in various courts of law pertaining to Questioned Documents, such as handwriting, type matters, printed matters, obliterations, erasures, additions and alterations, examination of inks, indented writings, latent writings, use of various equipments such as ESDA, VSC6000, Raman Spectrometer, Docucentre, Forensic XP, SEM etc.

DR. R.N. Khound

Dr. R.N. Khound is the Director, Directorate of Forensic science, Guwahati, Government of Assam. Having a master’s and doctorate in physics, he has been in the profession for the last 33 years.

Priyankar Ghosh

Priyankar Ghosh is the Director–in-Charge in the Central Forensic Science Laboratory, Directorate of Forensic Science Services, Ministry of Home Affairs, Government of India. Having a master’s degree in chemistry, he has been in the profession for the last 27 years.


Publisher, Dr. Robert O'Block, American College of Forensic Examiners.