Ceglia v. Zuckerberg et al

Filing 416

DECLARATION signed by Larry Stewart re 348 Order on Motion to Stay, Scheduling Conference, Oral Argument,,,,,,,,,,,, 414 Declaration filed by Paul D. Ceglia Expert Report. (Attachments: # 1 Supplement 46-55, # 2 Supplement 56-66, # 3 Supplement 67-90, # 4 Exhibit p. 1-82, # 5 Exhibit p. 83-167, # 6 Exhibit p. 168-229, # 7 Exhibit p. 230-290)(Boland, Dean)

Exhibit 24

Declaration of Larry F. Stewart

Exhibit 25

Declaration of Larry F. Stewart

J Forensic Sci, July 2009, Vol. 54, No. 4
doi: 10.1111/j.1556-4029.2009.01084.x
Available online at: www.blackwell-synergy.com

Commentary on: Berger-Karin C, Hendricks U, Geyer-Lippmann J. Comparison of natural and artificial aging of ballpoint
inks. J Forensic Sci 2008;53(4):989–92.
Sir,
We would like to comment on this study recently published in
JFS. It is a short technical note proposing an artificial aging technique for the dating of ballpoint pen inks. This is a very difficult
and controversial topic, and we are worried about the nature of this
paper. The scientific content can be misleading and can actually be
seriously questioned considering the following remarks:
• Two of the cited references are not relevant to the subject and
were probably not read by the authors. In the cited papers,
Aginsky (1) and Andermann and Neri (2) did not report about
solvent evaporation but about dyes analysis. Aginsky did actually publish several papers about solvent evaporation that could
have been cited instead (3–6).
• The data points on the figures are barely recognizable and the
curve functions are not formulated. What the authors actually
call a ‘‘very good correspondence’’ in Fig. 1 is unsubstantiated,
as the curves do not have the same shape at all (only the
decreasing-increasing tendencies are approximately the same).
The scales for the y and x axes do not correspond between the
compared figures. Moreover, the data point values, representing
single measurements are considerably different and the curve
fitting is obviously not good (i.e., the correlation coefficients
R2 are probably not approaching 1). It can also be noted that
Figs. 1a and 2b are exactly the same representation (redundancy). The fact that each data point was represented by three
correlated values (i.e., lozenge, square, and triangle) should have
been explained by the authors, as they apparently yield the same
information and add confusion to the figures.
• The SD measured on an ink standard (i.e., 0.06–0.07) represents
an error that is not negligible in comparison with the apparent
changes of phenoxyethanol in the figures. It is not specified if
the SD can be extrapolated to all data points; however, it would
be important to control that the error will not increase when the
measured quantity decreases as was observed by Horwitz (7) in
his evaluation of analytical methods.
• The authors analyzed 13 inks but showed results only for three
selected inks (numbered 356, 359, and 364). The variations
between the 13 different inks are probably considerable as was
demonstrated in another work published in the same journal (8).
This should be explained and discussed.
• The authors additionally proposed other compounds such as
phthalic acid ester to help in the age determination of inks.
However, they do not state precisely which aging phenomenon it
follows (e.g., polymerization, evaporation, etc.). The graphical
representation (Fig. 5a) does not help to understand what we are
supposed to see (i.e., representation of the increase and then
decrease of the peak area ratio of phthalic acid ester to phenoxyethanol). As ink 356 is a fast aging ink, the phenoxyethanol does
not diminish significantly after 1 month anymore as explained
earlier in the paper. So what is the meaning of such a curve? How
would the curve look when only representing the phthalic acid
ester peak area? The graphic representation is actually based on
only six single measurements (no error measurements). The relevance of this curve can therefore be questioned, and except for
Ó 2009 American Academy of Forensic Sciences

the maximum at about 400 days, the represented y-values
correspond to at least two x-values (i.e., two possible age determinations): for example, a value of 0.1 € 0.07 would correspond
similarly to approximately 0, 30, 190, or 750 days! This cannot
be valid. The accelerated aging curve (Fig. 5b) is again quite
different from the natural aging (Fig. 5a). The values obtained are
lower (and the scale is not the same for both figures).
The authors propose several ideas to differentiate fast aging and
slow aging inks but their experimental data is not validly represented
and ⁄ or discussed. These data are insufficient to draw any conclusions
about any potential of the method for ink dating purposes. Bügler
et al.’s (8) latest publication in the same journal offers, in contrast,
a very valuable and informative publication on the subject. We are
sorry to see this type of paper published while the influence of storage conditions on ink aging has not been addressed sufficiently in the
literature. This lack of information on the subject must be filled
before proposing such methods for practical caseworks. These are
preliminary and unconvincing results from development research performed in a laboratory on controlled samples without due warnings
about potential shortcomings. They cannot be used or even compared
with results obtained in real situations on uncontrolled specimens of
limited size, unknown composition, and undefined storage conditions.
This can leave an undeserved feeling that these methods are ready for
implementation when the task of ensuring their scientific validity is
still far away (9). We would like to emphasize the ethical guidelines
previously discussed by Brunelle and Cantu (10) in this journal and
their warning that forensic scientists should not attempt to examine
actual criminal or civil cases until they have been tested.
References
1. Aginsky VN. Comparative examination of inks by using instrumental
thin-layer chromatography and microspectrophotometry. J Forensic Sci
1993;38(5):1111–30.
2. Andermann T, Neri R. Solvent extraction techniques—possibilities for
dating ball point pen inks. Int J Forensic Doc Exam 1998;4(3):231–9.
3. Aginsky VN. Dating and characterizing writing, stamp, pad and jet printer inks by gas chromatography ⁄ mass spectrometry. Int J Forensic Doc
Exam 1996;2(2):103–16.
4. Aginsky VN. Some new ideas for dating ballpoint inks—a feasibility
study. J Forensic Sci 1993;38(5):1134–50.
5. Aginsky VN. Determination of the age of ballpoint pen ink by gas and
densitometric thin-layer chromatography. J Chromatography A 1994;
678:119–25.
6. Aginsky VN. Measuring ink extractability as a function of age—why
the relative aging approach is unreliable and why it is more correct to
measure ink volatile components than dyes. Int J Forensic Doc Exam
1998;4(3):214–30.
7. Horwitz W. Evaluation of analytical methods used for regulation of
foods and drugs. Anal Chem 1982;54(1):67–76A.
8. Bügler JH, Buchner H, Dallmayer A. Age determination of ballpoint
pen ink by thermal desorption and gas chromatography-mass spectrometry. J Forensic Sci 2008;53(4):982–8.
9. Weyermann C, Schiffer B, Margot P. A logical approach to ballpoint
ink dating. Sci Justice 2008;48(3):118–25.
10. Brunelle RL, Cantu AA. Training requirements and ethical responsibilities of forensic scientist performing ink dating examinations. J Forenisc
Sci 1987;32(6):1502–8.
CØline Weyermann,1 Ph.D.; Williams Mazzella,1 Ph.D.;
and Pierre Margot,1 Ph.D.
1
Institut de Police Scientifique, Lausanne University
Batochime, CH-1015 Lausanne, Switzerland
E-mail: [e-mail]

967

J Forensic Sci, July 2008, Vol. 53, No. 4
doi: 10.1111/j.1556-4029.2008.00770.x
Available online at: www.blackwell-synergy.com

TECHNICAL NOTE

Claudia Berger-Karin1; Ursula Hendriks,1 Ph.D.; and Jochen Geyer-Lippmann,1 Ph.D.

Comparison of Natural and Artificial Aging of
Ballpoint Inks

ABSTRACT: Solvent evaporation caused by aging from ballpoint inks was measured by gas chromatography ⁄ mass spectroscopy (GC ⁄ MS). The

sample preparation was carried out with two different thermal desorption systems. The results are compared. Thirteen inks were classified with regard
to their solvents, polymers, and additives. The variation of the aforementioned compounds caused by aging was monitored for naturally and artificially aged samples. In this paper, the results are compared and discussed with respect to forensic casework.

KEYWORDS: forensic science, age determination, artificial aging, ink, gas chromatography ⁄ mass spectroscopy, thermal desorption

In the last years the direct method of dating ink entries based on
the analyses of the solvent evaporation from the writing has been a
subject for several forensic investigations (1–6).
Recently Bügler et al. (6) published a method for age determinations of ballpoint inks by gas chromatography ⁄ mass spectroscopy
(GC ⁄ MS) based on sample extraction by thermal desorption in two
steps. It is postulated that the amount of phenoxyethanol (PE) in
fresh pen strokes evaporates at a moderate temperature whereas the
amount of PE which is included in the polymer matrix in older
pen strokes needs a higher extraction temperature. The method is
applicable if PE does not evaporate from the writing too fast.
The following paper describes a variation of the method.
Material and Methods
Equipment
For thermal desorption of the ink samples on paper two different
thermal desorption units were used:
• Atas Desorption System Optic III with Linex Injector and cold
trap, equipped with a CombiPAL autosampler, connected to a
Thermoelectron GC ⁄ MS-system Trace GC ⁄ DSQ.
• Markes Desorption System Unity ⁄ Ultra TD with cold trap, connected to an Agilent 6890N GC ⁄ MS system.
In the Atas system the sample is placed directly into the liner
where thermal desorption takes place. The gas is frozen out in a
part of the column which is led through the cold trap cooled by
liquid nitrogen. In the Markes system thermal desorption is carried
out in glass tubes. The gas is gathered in a cold trap which is
cooled by a peltier element.
The preconditioning of the glass tubes is performed by heating
the tubes at 300°C for 30 min.
1
Der Polizeipräsident in Berlin, Landeskriminalamt, Kompetenzzentrum,
Kriminaltechnik KT 43, Tempelhofer Damm 12, D-12101 Berlin, Germany.
Received 31 Mar. 2007; and in revised form 11 Aug. 2007; accepted 1
Dec. 2007.

Ó 2008 American Academy of Forensic Sciences

For the monitoring of the instrument performance 1 lL of a
solution of PE (Merck, purity >99%), 2-decanone, 2,3-dimethylnaphtalin and n-pentadecan in acetone (Merck, purity >99.8%) on
paper was analyzed using the same conditions under which the
analyses of ballpoint inks were carried out.
Desorption of Ink Samples
Desorption Method—A piece of pen stroke on paper (length:
0.7–1.0 cm) was cut out and placed into the liner (Atas) or the
thermal desorption tube (Markes). The sample was heated in three
steps at 100°C (15 min), 140°C (15 min), and 200°C (10 min) and
the desorption gas was collected in the cold trap at )80°C (Atas)
or )15°C (Markes). After every thermodesorption step the sample
was removed from the heating system. By heating the cold trap
(300°C ⁄ min: Atas; 100°C ⁄ min: Markes) the desorption gas was
given onto the column for analysis at the following conditions:
Column: ZB5ms Guardian
Carrier Gas: He, 1.2 mL ⁄ min
Oven program: 100°C, 3 min; 100–200°C, 15°C ⁄ min; 200–320°C,
25°C ⁄ min; 320°C, 6 min

Integration of the signals was performed on chromatograms of
the single ion mode.
Screening of Contents—In order to find criteria to differentiate
between the inks, screenings of the volatile compounds were
performed.
For the screening of the volatile contents of the ballpoint inks,
ink samples on paper were put on glass pins which were placed
into the glass tubes and heated at 240°C. The collection of the
gas and the GC ⁄ MS-analyses followed the aforementioned
conditions.
Accelerated Aging
For accelerated aging of ballpoint inks, samples were cut out
(0.7–1.0 cm of the pen strokes) and put into an oven at 45°C.
989

990

JOURNAL OF FORENSIC SCIENCES

(a)

(b)

(a)

(b)

FIG. 1—(a) Validation of the two systems (Atas). (b) Validation of the
two systems (Markes).

FIG. 2—(a) Fast aging ballpoint ink. (b) Slowly aging ballpoint ink (see
also Fig. 1a).

In a time range from 2 to 33 1 ⁄ 3 days the loss of the solvents
and the variation of polymer compounds and plasticiziers was
measured.

Accelerated Aging

Results
Validation of the Systems
Naturally aged samples of the same ink were analyzed on the
Atas and the Markes system. In all cases only single measurements
were made.
The standard deviation was measured by analyzing samples of
an ink standard with a natural age of 18–21 days once a week. The
standard deviation of 10 measurements was 0.06–0.07.
The graphs for the variation of PE, measured at the three temperatures shows a very good correspondence for the two systems.
So it is possible to control the reliability of the results of one system by the other (Fig. 1).

The results obtained by analyses at the three temperatures for the
samples from accelerated aging (Fig. 3) correspond to those of the
naturally aged inks (Fig. 2b).
The loss of PE caused by accelerated aging of ink samples of
defined natural ages is shown in Figs. 4a and 4b. Accelerating
aging in three steps was carried out with ink samples with a natural
age of 3 months (storage at 45°C for 3, 6, and 17 days) and 1 year
(storage at 45°C for 3, 6, and 9 days). For writings of unknown
age the amount of PE of the original sample and the variation of
this amount by three steps of heating allow estimations of the original age of the writing.

Natural Aging
The main compound which gives information about the aging
of a ballpoint ink is PE which is used as a solvent in nearly all
inks. The loss of PE was monitored for natural and artificial
aging of inks in three thermal desorption steps at 100, 140, and
200°C. The amounts of outgassing PE at each temperature was
brought into relation ratio to the total amount of PE measured
in the three steps. These mass-independent results corresponded
to those which were reported by Bügler et al. (6) for fast
aging and slowly aging inks. The fast aging inks show a loss of
PE within the first month while the slowly aging products lose
the solvent during a time of 3 months or more (Figs. 2a and
2b).

FIG. 3—Artificial aging of ink 364 at 45°C.

BERGER-KARIN ET AL. • AGE DETERMINATION OF BALLPOINT INKS

(a)

(b)

FIG. 4—(a) Artificial aging of a 3-month-old ink sample. (b) Artificial
aging of a 1-year-old ink sample.

991

(a)

(b)

FIG. 5—(a) Fast aging ink 356—Natural aging: phthalic acid
ester ⁄ phthalic acid ester + PE. (b) Fast aging ink 356—Artificial aging:
phthalic acid ester ⁄ phthalic acid ester + PE.

Estimations on the Age of Writings Based on other Compounds
in Addition to Phenoxyethanol
For fast aging inks which contain large amounts of phenoxyethoxyethanol, phtalic acid esters, or phtalic anhydride, estimations
about the age of questioned writings are possible based on the variation of these compounds by aging of the writing.
Seven of the ballpoint inks analyzed show characteristic graphs
for the variation of phthalic anhydride or phthalic acid esters by
aging of the pen strokes. This result, which is obtained for the naturally aged inks, corresponds to that of the artificially aged samples
of the same inks (Figs. 5a and 5b).
For five inks which contain a huge amount of phenoxyethoxyethanol the decrease of this solvent at 140°C referred to the amount
of PE allowed estimations on the age of the pen strokes (Fig. 6).
Discussion
As reported by several authors in the past (1–6), the loss of PE
can be used as a reference to the age of a writing produced with
ballpoint ink.
It is possible to differentiate between inks which lose most of
the solvent very quickly (within 1 month) and inks which lose the
biggest amount of the solvent within 3 months or more.
In our laboratory, these results could be verified by using thermodesorption GC ⁄ MS-chromatography with two GC ⁄ MS-systems
with different thermal desorption systems. The sample preparation
and the conditions of the analyses were the same, and the results
obtained from the two systems, i.e., the amounts of PE detected at
the three temperatures in relation to the whole amount of PE,
showed a good correspondence.

FIG. 6—Ink 356—Decrease of phenoxyethoxyethanol.

If either of the thermodesorption GC-MS methods is applied to
forensic casework, the results may not give the necessary information to estimate the age of a questioned ink. This is possible if
samples of the same ink are measured three or four times within a
larger range of time (1–3 months). The storage time can be shortened by accelerated aging at 45°C (3–33 1 ⁄ 3 days). For this purpose, tests of accelerated aging at 45°C of fresh and naturally aged
older samples were performed.
It was shown that the decrease of PE in slowly aging inks of
artificially aged samples corresponds well to that of natural aging
and allows conclusions on the original age of the questioned
writing.

992

JOURNAL OF FORENSIC SCIENCES

The results concerning the outgassing of PE cause some limitations to forensic case work if the samples delivered for analysis are
of the fast aging type.
In that case the variation of other contents of the ink caused by
aging can give more information. For seven inks which contained
small amounts of plasticizers or phthalic anhydride as polymer a
variation of these compounds was obvious which allowed further
estimations on the age of the writing. Further studies will be carried
out to support this result.
If the loss of phenoxyethoxyethanol in relation to the decrease of
PE in inks which contain a huge amount of phenoxyethoxyethanol
is monitored, a variation of phenoxyethoxyethanol can be noticed
which gives additional information concerning the age of the ink.
References
1. Aginski V. Comparative examination of inks by using instrumental thinlayer chromatography and microspectrophotometry. J Forensic Sci
1993;38(5):1111–30.
2. Andermann T, Neri R. Solvent extraction techniques–possibilities of
forensic document examiners. Int J Forensic Doc Exam 1998;4:231–9.

3. Stewart LF. Ballpoint ink age determination by volatile component comparison–preliminary study. J Forensic Sci 1985;30:405–11.
4. Gaudreau M, Brazeau L. Ink dating using a solvent loss ratio method. Proceedings of the 60th Annual Conference of the American Society of
Questioned Document Examiners; 2002 Aug 14–19; San Diego, CA. Long
Beach, CA: American Society of Questioned Document Examiners, 2002.
5. Andrasko J. Age determination of ballpoint pen inks by GC ⁄ MS using
SPME and extraction methods. Proceedings of the Third European Academy of Forensic Science Meeting; 2003 Sept 22-23; Istanbul, Turkey.
Istanbul, Turkey: Institute of Forensic Sciences of Istanbul University,
2003.
6. Bügler JH, Buchner H, Dallmayer A. Characterisation of ballpoint pen
inks by thermal desorption and gas chromatography-mass spectrometry.
J Forensic Sci 2005;50(5):1209–14.
Additional information and reprint requests:
Ursula Hendriks, Ph.D.
Der Polizeipräsident in Berlin
LKA KT 43
Tempelhofer Damm 12
D-12101 Berlin
Germany
E-mail: [e-mail]

Exhibit 26

Declaration of Larry F. Stewart

Exhibit 27

Declaration of Larry F. Stewart

Forensic Science International 210 (2011) 52–62

Contents lists available at ScienceDirect

Forensic Science International
journal homepage: www.elsevier.com/locate/forsciint

Minimum requirements for application of ink dating methods based on
solvent analysis in casework
´
¨
¨
Celine Weyermann a,*, Joseph Almog b, Jurgen Bugler c, Antonio A. Cantu d,1
a

ˆtochime, CH-1015 Lausanne, Switzerland
Institut de Police Scientifique, University of Lausanne, Ba
Casali Institute of Applied Chemistry, The Hebrew University of Jerusalem, Jerusalem, Israel
c
Institute of Forensic Sciences, Bavarian State Bureau of Investigation, Munich, Germany
d
Scientific Consultant, Falls Church, VA, USA
b

A R T I C L E I N F O

A B S T R A C T

Article history:
Received 11 November 2010
Received in revised form 21 January 2011
Accepted 25 January 2011
Available online 4 March 2011

Several ink dating methods based on solvents analysis using gas chromatography/mass spectrometry
(GC/MS) were proposed in the last decades. These methods follow the drying of solvents from ballpoint
pen inks on paper and seem very promising. However, several questions arose over the last few years
among questioned documents examiners regarding the transparency and reproducibility of the
proposed techniques. These questions should be carefully studied for accurate and ethical application of
this methodology in casework. Inspired by a real investigation involving ink dating, the present paper
discusses this particular issue throughout four main topics: aging processes, dating methods, validation
procedures and data interpretation. This work presents a wide picture of the ink dating field, warns about
potential shortcomings and also proposes some solutions to avoid reporting errors in court.
ß 2011 Elsevier Ireland Ltd. All rights reserved.

Keywords:
Forensic sciences
Questioned documents
Ink dating
Solvent drying
Aging
Method validation
Interpretation

1. Introduction
Determining when an ink entry was produced on a document
has always been a major issue in the examination of questioned
documents. For this reason many scientists aimed at developing
dating methods along the years [1–5]. There are three main
approaches for ink dating on documents. The first approach is
based on the analysis of ink stable components that are specific to a
certain period in time. Production methods and compositions
change and evolve with time following new industrial developments and processes. This approach is generally named in the
literature ‘static approach’ because the measured parameters are
almost invariable in time [2]. It allows the determination of the
first possible date of existence for a given composition of ink and
may thus highlight anachronisms. Knowledge of some major
historical changes in ink manufacturing is available (e.g.,
introduction dates of the major classes of compounds and dates
of major changes in formulation). However, most knowledge of
changes is proprietary industrial information and not readily
available. This is probably the reason why only the US Secret

* Corresponding author. [phone].
E-mail address: [e-mail] (C. Weyermann).
1
Retired U.S. Secret Service.
0379-0738/$ – see front matter ß 2011 Elsevier Ireland Ltd. All rights reserved.
doi:10.1016/j.forsciint.2011.01.034

Service (Washington, USA) and the LKA Bayern (Munich, Germany)
reported having extensive ink samples and databases [6,7].
Additionally a program started in the mid 1970s in the USA, in
collaboration with the ink manufacturers, for introducing annually
modified tags to inks [2], but it covered only a fraction of the whole
ink market. The second approach, addressed as the ‘absolute
dynamic approach’ [3] is based on aging processes of ink on
documents. It is assumed that ink does not age in the cartridge
[8,9], but only after it is placed on paper where dyes fade, solvents
diffuse and evaporate, and resins polymerise. Aging processes of
ink follow complex pathways that are considerably influenced by
several factors other than time, which may accelerate or slow
down the aging. The influencing factors can be ordered in three
main classes [4,10]: (i) initial composition of the ink (in the
cartridge), (ii) physical and chemical properties of the substrate
(paper composition, porosity and coatings) and (iii) storage
conditions (temperature, light, air flux, humidity, neighbouring
material, etc.). In practice, no information on these factors is
generally available. This is why the determination of the absolute
age of an ink entry remains truly difficult. Measured changes are
reported as a function of time in order to establish an aging curve
or a portion of it and the objective is therefore more the
determination of a time range than a precise date. The time scale
considered can significantly vary depending on the measured
parameters. For example, while solvents disappear from the ink

53

C. Weyermann et al. / Forensic Science International 210 (2011) 52–62

very quickly, dyes degradation occurs more slowly. The third
approach aims at determining the relative age of a document in
comparison to others (i.e., to order them in chronological
sequence) and is referred to as the ‘relative dynamic approach’
[3]. The comparison of the extent of ink aging may help
reconstructing the sequence of apposition of ink entries on
documents. This can only be applied for inks of the same formula
stored under the same conditions on the same type of paper (e.g.
diaries) [11]. That is, it applies to inks that only differ in the time
they were placed on paper. The general evolution of the aging
curve must be known [4]; for example if a decrease of the aging
parameter is expected as a function of time, it is imperative to
insure it will never increase whatever the conditions.
The most promising methods in the 1980s involved the analysis
of sequential extraction of dyes using thin layer chromatography
(TLC) [11–20]. It was based on the changes in the extractability of
the ink supposedly caused by the hardening of the resins [10,21–
24]. The use of this technique in caseworks was reported in the
literature [18,25], but it was followed by a vigorous controversy
among the scientific community about the limitations of this
approach [5,26–42]. Several researchers tried reproducing the
results obtained in previous studies and reported the methods to
be unreliable [28,34–36], while other scientists debated about the
necessity for inter-laboratory validation before their use in
casework [4,27,31–33,38,41].
During the last decades interest has shifted to methods based
on sequential extraction and analysis of ink volatile components by
gas chromatography (GC) coupled with mass spectrometry (MS) or
other detectors [17,18,34,44–58], which seemed more promising
in terms of reproducibility. Although some forensic laboratories do
already apply such ink dating methods in practice, several issues
remain open including the inter-laboratory validation. Triggered
by a recent ink dating case in Israel, this article aimed at clarifying
the ink dating field for justice purposes and guiding scientists
through validation of their methodologies, while highlighting
practical limitations. It was earlier acknowledged that a central
unsolved problem in the field of questioned documents examination is the unequivocal determination of their age [59]. Despite the
significant progress in analytical techniques and several published
propositions for ink dating, the field of document examiners is still
divided about this issue, for reasons that will be clarified and
discussed throughout this article. The purpose of this work is to
give the status of the various ink dating methods that are based on
the analysis of an ink’s solvent components, show their limitations,
and suggest methods to improve them. It is subdivided in four
main sections as follows: Section 2: ink drying principles; Section
3: ink dating methods; Section 4: methods validation; Section 5:
ink dating interpretation.
2. Ink drying principles
The dating methods considered in this article all focus on the
analysis of solvents from ink strokes on paper. It was observed
early that the amounts of solvents in the ink strokes decreased as a
function of time [44], according to the following equation [50,51]
for the relative peak area (RPA):
RPA ¼ p1 þ p2 Á eÀðt= p3 Þ

0:5

þ p4 Á eÀðt= p5 Þ

0:5

(1)

where p1 is an additive constant, p2 and p4 provides the
contribution of the first and second exponential, and p3 and p5
are time constants associated with the exponential. The ink drying
processes were earlier described in the literature as two separated
falling rate phases [51]. The first exponential represents the fast
falling rate of drying (rapid solvent evaporation and diffusion into
the paper) and the second exponential represents the slow falling

volatilization

ink
paper

volatilization
Fig. 1. Simultaneous ink drying processes on paper: the ballpoint pen solvent
molecules volatilize (evaporate), diffuse (migrate and penetrate via absorption) and
are adsorbed by the paper substrate. While grey arrows represent volatilization,
black arrows represents diffusion, migration, penetration, absorption and
adsorption.

rate of drying (slower evaporation and diffusion processes) [50,51].
Low amounts of solvents may even stay trapped in the ink matrix
for years [17,45,52]. Based on previous researches, the following
theoretical aging model can be formulated: several processes occur
simultaneously when ink is placed on paper, such as evaporation of
solvents in the ambient air, diffusion/absorption in the paper and
adsorption by the paper substrate (Fig. 1). Volatilization occurs
actually in the ink surface, in the paper surface near the ink and in
the paper surface the opposite from the ink. Moreover the solvent
molecules may diffuse into adjacent surfaces (for example in a
stack of paper sheets) [51].
The compound phenoxyethanol is the most widespread solvent
in ballpoint pen inks [57,60,61] and therefore most dating methods
finally focused exclusively on the analysis of this specific substance
(Fig. 2).
As explained above, ink aging pathways and rates are
significantly influenced by a number of factors that may slow
down or accelerate the phenomenon [42,61]. These parameters
must therefore be extensively studied before a conclusion can be
drawn on the absolute age of an ink entry.
2.1. Ink formulation
The influence of the initial ink composition on the aging rates of
inks is very important [23,45,56]. Two aspects must be considered:
the compounds (dyes, resins, solvents, and additives) and their
relative amounts (initial solvent quantity in the ink formulation).
¨
Bugler et al. actually suggested that the type of resins influenced
the aging rates as they observed the presence of acetophenone–
formaldehyde–resin in ‘slowly aging inks’ [56]. It is therefore very
important to have a precise knowledge of the ink market (for
example through an ink database) in order to develop a method on
selected representative inks.
2.2. Initial ink quantity
The initial quantity of solvents in an ink stroke also influences
significantly the aging process (i.e., the drying of the ink). For
example, it is dependent on the writing pressure (i.e., thickness of

OH

m.w.

138.2 g/mol

b.p.

247°C

viscosity at 25°C

O

21.5 cP

Fig. 2. Structure formula, molecular weight, boiling point and viscosity of the
solvent phenoxyethanol.

54

C. Weyermann et al. / Forensic Science International 210 (2011) 52–62

Fig. 5. Solvents diffusion from two ink entries: (left) diffusion away from a straight
line and (right) diffusion inside the loop of the letter ‘o’. The solvent concentration
may be significantly higher in 1 cm of the loop compared to 1 cm of the straight line.

Fig. 3. Superimposed curves for the evaporation of 10, 20, 40, 60, and 100 ml of the
solvent ethoxyethanol from paper: the loss of weight in micrograms (steps of
5000 mg) is presented as a function of the time in hours. Lower evaporation rates
were observed when smaller volumes of solvents were initially deposited on paper
[61].

ink) or and/or also on the size of the ball in the ballpoint pen. Lower
evaporation rates were observed for smaller volumes of solvents
on paper (Fig. 3), when the solvent ethoxyethanol was placed on
the paper surface using a micropipette. With larger quantities of
solvent applied to the paper, a larger accessible surface area will be
available for evaporation (Fig. 4), and thus a higher evaporation
rate will be observed.
This is problematic as the relative content of phenoxyethanol
varies considerably among different ballpoint inks [38]. The size of
the ball of the ballpoint pen and the pressure applied while writing,
both of which determine the thickness and depth of the ink line,
respectively, also affect the initial quantity of phenoxyethanol
found in 1 plug or 1 cm of ink line. Moreover, in research works, ink
entries are generally drawn as straight lines, allowing solvents to
diffuse away from the stroke. Questioned documents will most
probably carry texts with curved lines from any alphabet. For

example, in the letter ‘‘o’’, the solvents will diffuse to some extent
away from the letter and partly inside the ring. Higher quantities of
solvents may be found in letters with dense lines compared to a
straight line of the same length (Fig. 5). This represents a major
problem. When extracting 1 cm ink lines from different letters, one
is not guaranteed to have always the same solvent quantity.
Aginsky tried to minimize this effect by calculating a mass
¨
invariant ratio between two samples [34,52]. Bugler et al. even
tested the mass independence of a given aging parameter by
analysing ink entries of different lengths on the same paper [56].
For example, if 2 cm of an ink line containing 0.3 mg of
phenoxyethanol per cm was analysed, one would record twice
as much phenoxyethanol than in 1 cm (Table 1). However if you
calculate a ratio between two compounds found in the ink [50,52]
or between two sequential extractions of the same ink entry
[52,56], the ratio should be the same regardless of the length of the
ink line.
However, only the length independence between two samples of
the same entry is guaranteed, and not the mass independence, as
pressure (i.e., thickness) and density (i.e., distribution) vary along a
stroke (Fig. 5) [56].
In practice, it is impossible to ensure the homogeneity of the ink
applied on paper, thus the influence of such parameters on the
solvents aging kinetics must be quantified. Dating would then be
possible only if the errors provoked by different solvent quantities
resulting from the above situations were smaller than expected
changes as a function of the age. This actually requires more
research than was published so far.
2.3. Paper type
The influence of substrate structure (paper type) on the drying
process should not be underestimated, as their porosity can differ
quite widely within a same sheet of paper (pores diameter
between 0.05 and 10 mm). Molecular diffusion, Knudsen (through
pore) diffusion, surface diffusion, capillary condensation of vapors,
physisorption (absorption and adsorption), chemisorption, migration and evaporation will all be influenced by the porous structure,
the fibers (e.g., cellulose fibrils) and the paper chemistry (alkaline

Table 1
The parameters M1 and M2 are absolute quantities of phenoxyethanol and are
dependent of the length of the stroke, while calculating a ratio between these two
parameters yield a length independent feature.

Fig. 4. Visible surface area [cm2] taken up by the solvents ethoxyethoxyethanol (E),
dipropylene glycol (D) and phenoxyethanol (P) a short time after deposition on
paper with a micropipette, as functions of the volume deposited [ml]. The surface
areas increased with the volume, but were also influenced by the viscosity, density,
hygroscopicity and volatility of the solvents [61].

Ink line
length (cm)

First
parameter

Second
parameter

Ratio (Table 4; Eq. (3))

M1 (ng)

M2 (ng)

M1Á100%/(M1 + M2)

1
2

30
60

70
140

30
30

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C. Weyermann et al. / Forensic Science International 210 (2011) 52–62
Table 2
Procedure to determine the rate of decrease of volatile components (R) in inks on documents.
Method 1

Sample set 1 (normal)

Sampling
Treatment
Extraction

10 microdiscs (1 mm diameter) of the ink on paper
Moderate heating (e.g. 70 8C, 1 h [52] or 2 h [49])

No treatment

10 ml [52] or 15 ml [49] of appropriate solvent (e.g. acetonitrile with an internal standard)
1 ml of extract analysed by GC/MS (SIM mode)

Analysis
Results

Sample set 2 (artificially aged)

P = mass of solvent

PT = mass of solvent

Eq. (2)

or acidic, fillers, detergents, additives, etc.). Aginsky stated having
studied the influence of paper type ([52], footnote 10) reporting it
¨
to be negligible, but no details have been disclosed. Bugler et al.
also studied the influence of the paper type on the aging process
and reported a strong dependence on paper type for his method
[56].
2.4. Storage and environmental conditions
Due to the fact that diffusion and evaporation mechanisms play
such an important role in the drying of solvents on porous media, a
wealth of external factors must be taken into account. Among
these are temperature (of air, substrate, ink), solvents’ vapour
pressure, humidity, air movement (laboratory, cabinets), the
properties of solvents mixtures (vaporization of the solvent
mixture, viscosity), and those properties of ink and paper that
could affect heat transfer and mass transfer coefficients. On that
aspect, Aginsky wrote that his results ‘suggest that the Q
(questioned) writing is old (. . .) on condition that the document
bearing the Q writing has been stored under normal environmental
conditions, for example, under room temperature and constant
humidity and light conditions [52]’. Lower temperatures and air
flows will slow down the drying process. Moreover, room
temperatures may vary considerably between summer and winter
(except for air conditioned rooms), whereas humidity is rarely
constant even in an air conditioned environment.
Possible contamination of old strokes through solvent
migration from fresh strokes on adjacent sheets of paper should
also be taken into account [47,51,61,62]. It was observed that
solvents from a fresh stroke (t = 0) can very efficiently migrate to
adjacent sheets of paper in a pile. It was found that the
quantities of solvent involved in this migration exceeded those
found in a stroke after two weeks [51], so that conversely,
contamination of a stroke by migration must be taken into
account for the dating of ink entries by solvents quantification.
Paper blank analysis will help reduce the risk [46]; however the
contamination may be very local [62]. Since solvents diffuse
from the ink stroke into the paper, the paper blank should not be
sampled too close to the ink entries [51]. One has to be
particularly careful regarding the way documents are stored,
due to the possibility of contamination (in a notebook or file
folder), but also because of the suppression or reduction of
drying processes in tightly sealed (e.g., glass vial) [61] or semihermetic (e.g. plastic cover) situations respectively. Additional
measurements are needed to follow the drying of inks on papers
for long storage times under such conditions. Storage conditions
were barely studied up to now in spite of their crucial influence
on aging kinetics. Most reports contain data collected from
documents which have been stored only under laboratory
conditions. From a validation point of view it is therefore
important in practice to apply a method within its range of
applicability and to state exactly under which circumstance the
results are valid.

R(%) = [(P À PT)/P]Á100 [49,52]

3. Dating methods based on solvents analysis described in the
literature
First proposed by Stewart [44], further developments of dating
methods based on solvents analysis were inspired by the works of
Cantu on sequential extraction [11] and artificial aging [12]. Aginsky
proposed two multi-staged ‘absolute dynamic dating methods’
[34,45,52]. These methods’ principles were briefly addressed in
two preceding papers [17,18]. Aginsky’s methodology [52] is based
on the supposition that as ink ages, its resins harden (solidify) and
subsequently the ink solvent extractability decreases over time [45].
Solvents (volatile ink vehicles) are analysed and more specifically the
rate of decrease of solvents amounts (method 1 described below) and
the rate of decrease of solvents extractability (method 2 described
below). Gaudreau and Brazeau of the Forensic Document Examination Section of the Canada Border Services Agency reported in a
conference presentation the use of a dating method based on the
same principles [49] (modification of method 1 described below). More
¨
recently, Bugler et al. described a method based on the same
principles, but involving a different sample preparation
[55,56,63,64] that has been implemented by several laboratories
in Germany, Switzerland and Canada (modification of method 2
described below as method 3). The first step of dating measurements
generally consists of detection and identification of the volatile
components of the ink (described, for example, as procedure 1 in
[52]). As explained above, the ink component used for dating is
phenoxyethanol, since it is the most commonly found in ballpoint
pen inks [51,56,57].
Additionally, some recent developments based on previous tests
[17,44,50] proposed to calculate the loss of phenoxyethanol in
relation to a stable compound quantification such as a dye as a
function of time [65–67]. For the moment no further information
were published about this alternative approach and it will therefore
not be directly treated in this paper. However the same principles
would apply to their potential future application in practical cases.
3.1. Method 1
Described as Rate of decrease of volatile components R% by
Aginsky [52] and Solvent loss ratio by Gaudreau and Brazeau [49].
Aginsky’s procedure [52] implies the removing of two sets of
samples each consisting of 10 microdiscs (about 1 mm in diameter)

Table 3
Summary of R thresholds values defined in the literature and in conference
proceedings.
Aging
parameter (%)

Threshold
value

Ink entry age

Literature

R
R

!20
!50

Fresh
Less than 6 months

R

!25

Less than 1 year

Aginsky [52]
Gaudreau and
Brazeau [49]
Gaudreau and
Brazeau [49]

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C. Weyermann et al. / Forensic Science International 210 (2011) 52–62

Table 4
Procedure to determine the rate of decrease of solvent extractability (D) of inks from documents described by Aginsky [52].
Method 2

Sample 1 (normal)

Sample 2 (artificially aged)

Sampling
Treatment
Weak extraction

10 microdiscs (1-mm diameter) of the ink on paper
Moderate heating (e.g. 70 8C, 60 min)

No treatment

10 ml of an appropriate weak solvent (e.g., carbon tetrachloride)

Analysis 1
Results 1
Strong extraction

Extract analysed by GC/MS
Mweak = mass of solvent

Mweak = mass of solvent

After drying, in 10 ml of an appropriate strong solvent (e.g. chloroform)

Analysis 2
Results 2
Eq. (3)

Extract analysed by GC/MS
Mstrong = mass of solvent
P = 100Á[Mweak/(Mweak + Mstrong)]

Eq. (4)

of the ink on paper using a boring device (also called micro-punch
device). Sample set 1 is placed in a vial and extracted with 10 ml of an
appropriate solvent with an internal standard. 1 ml of the extract is
analysed by GC/MS (SIM mode with detector set to monitor ions
which are specific for the identified substances and internal
standard). The mass of the ink solvent detected (i.e. the ink aging
parameter P) is calculated by means of the internal standard method.
Sample set 2 is heated moderately and analysed using the same
procedure as for sample set 1 to determine the mass of the ink
solvent after heating (i.e. the ink aging parameter PT). The rate of
decrease of volatile components is calculated using Eq. (2) in Table 2.
If the value of R is ca. 20% or larger, it shows (on condition that the
content of the analysed ink’s solvent is not too small, at least, not less
than 1 ng per sample) that the natural aging of the ink analysed is
still in progress, i.e., the ink writing is fresh (Table 2) [52]. In his paper
[52], Aginsky proposed an alternative ink aging parameter P if any
volatile solid component of the ink was detected: P = ratio solvent
peak areas to non-volatile component peak areas. However this
method was not mentioned again in later publications.
Gaudreau and Brazeau reported using a similar method to
determine the approximate age of an ink entry in conference
proceedings [49]. Two sample sets each containing 10 plugs of ink
are removed. One sample set is heated at 70 8C for 2 h and then
both are extracted with 15 ml acetonitrile containing internal
standard for 5 min. Using Eq. (2) in Table 2, the authors determined
the following threshold values for phenoxyethanol: R ! 50% and
25% (including error) allowing to state that ink has been applied to
paper less than six months (150 days) and less than one year (300
days) prior to the test respectively (Table 3).
As of today, nobody else reported in the literature using this
method. However, Andrasko presented a modified solvent loss
ratio technique involving a different sample preparation (solidphase microextraction) [46,47] that was able to reveal if an ink is
fresh (4–6 months old at most). He later communicated his strong
doubts about the feasibility of such ink dating methods stating that
the method he had presented was unreliable and that the results
were not reproducible.2 A solid-phase microextraction method
was also studied by Brazeau and Gaudreau [54]. It should be noted
that this method requires that both the heated and unheated
samples have the same or nearly the same amount of ink. The
method is not independent of the amount or length of ink sampled.
3.2. Method 2
Described as rate of decrease of solvents extractability D% by
Aginsky [52].
2

Personal communication from J. Andrasko, 2003.

Mstrong = mass of solvent
PT (%) = 100Á[Mweak/(Mweak + Mstrong)]
D (%) = P À PT [52]

According to Aginsky’s report [52], two samples, each of 1 cm
slivers of the ink on paper are removed using a sharp scalpel.
Sample 1 is placed in a vial and extracted with 10 ml of a ‘slowly
extracting weak’ solvent. 1 ml of the extract is analysed by GC/MS
(SIM mode with detector set to monitor ions which are specific for
the identified substances and internal standard). The sample is
removed, dried, placed in another vial and extracted with 10 ml of a
‘fast extracting strong’ solvent. 1 ml of the extract is analysed by
GC/MS (same analysis settings). The mass of solvent in each extract
(Mweak and Mstrong) are calculated by means of the internal
standard method and the percent of the solvent mass extracted in
the weak solvent (P) is calculated using Eq. (3) in Table 4. Sample 2
is then heated moderately and analysed using the same procedure
as for sample 1 in order to determine the percent of extraction after
heating (PT). The distance (D) between the value P and PT is
calculated using Eq. (4) in Table 4. Method 2 is actually an upgrade
of method 1, as the total amount of extract Mweak + Mstrong (Table 4)
should theoretically have the same value as P (Table 2). Therefore
the final R% can be extrapolated from the raw results obtained by
method 2, without additional analyses.
Aginsky summarized: If the value of D is ca. 15% or larger, it shows
that the natural aging of the ink analysed has not levelled off yet, i.e.,
that the ink writing is fresh [52]. The following thresholds
definitions were proposed in the literature in 1996 [52]:
 D > ca. 15% – It suggests that the questioned writing is fresh, i.e.
it is less than eight-month old. If such a result has been obtained
for a questioned document dated, e.g. by over a year preceding
the analysis, the examiner can state with confidence that this
document has been backdated.
 D < ca. 10% – It suggests that the questioned writing is old, that is
its age is larger than ca. two months, on condition that the
document bearing the questioned writing has been stored under
normal environmental conditions, for example, under room
temperature and constant humidity and light conditions. It
should also be stressed that such results can also mean that the
questioned ink’s binder is not capable of cross-linking or
undergoing other processes of ‘solidification’ due to aging
(though there are very few such inks on the market).
 ca. 10% < D < ca. 15% – This means that additional samples of the
questioned entry should be taken (if enough ink is available) to
ascertain statistically if the mean of the D values obtained are
closer to 10% or 15%; in this case, the conclusion on whether the ink
in question is fresh or old is made with a certain degree of
confidence.
It was then specified in an appendix to the article [52] that if, in a
real case situation, a necessity arises to narrow the interval

57

C. Weyermann et al. / Forensic Science International 210 (2011) 52–62

100

Extraction Percentage (P)

90
80

fresh ink:
D > 15%

70

P

60

D

50

PT

40

old ink:
D < 10%

30
20

P

10

PT
D

0
0

1

2

3

4

5

6

7

8

9

10

Time / months
Fig. 6. Graphical presentation of the threshold values proposed by Aginsky [33] to
determine a time frame within which a questioned entry has been actually written.

Table 5
Summary of D threshold values defined in the literature and in conference
proceedings.
Aging
parameter (%)

Threshold
value

Ink entry age

Literature

D
D

ca. >15
ca. <10

Less than 8 months
More than 2 months

D

ca. >10
ca. <15
!20
5

More analyses

Aginsky [52]
Aginsky [52]
proficiency
Aginsky [52]

Less than 5 months
More than 6 months

Aginsky [52]
Aginsky [52]

Less
Less
Less
Less
Less

Aginsky
Aginsky
Aginsky
Aginsky
Aginsky

D
D
D
D
D
D
D

!18
!12
!8
!6
!4

than
than
than
than
than

6 months
8 months
12 months
18 months
24 months

[45]
[45]
[45]
[45]
[45]

comprising the real age of the ink in question, there were at least two
possibilities for this: (1) the ink formula is known and reference
samples may be prepared; (2) further thresholds determination as
follows:
 D ! 20% corresponds to ballpoint inks younger than 5 months.
 D 5% corresponds to ballpoint inks older than approximately 6
months.

New upper-threshold values were later presented in a
conference proceeding in 2002 (Table 4) [45].
This D parameter is then used to ascertain that the aging of the
ink sample has not stopped yet (Fig. 6). The principle follows the
idea that, when ink is fresh, P is high and PT is lower (then the
difference D is high and the sample is still drying). When the ink is
old, P is low and PT is also low (then the difference D is low and the
sample decreased its rate of drying).
The threshold values were defined using different ballpoint
pens. If the type is not always reported in the literature, the
number of pens was specified: between 30 and 50 [45]; 64 [49] and
up to 85 [56]. Thus the influence of ink formulation was to some
¨
extent tested, particularly in the work of Bugler et al. [56] who
selected representative inks from the ink library at the Forensic
Science Institute of The Bavarian Bureau of Investigation. As a
consequence, the influence of the initial quantity of phenoxyethanol was also evaluated. This is why only an upper-threshold
indicating the maximum age of an ink may be used [45,49,56]. The
presence of a high quantity of phenoxyethanol or the finding of a
high aging parameter may indicate a fresh ink, whereas its absence
does not allow any conclusion about the age [56] (see detailed
explanations below) (Table 5).
No published account from other authors reported using this
specific method. However, a method based on the same principles,
but involving a different sample preparation, was reported
recently in the literature and is described below [56,60,63,64].
3.3. Method 3
¨
Described as Ink age assessment procedure by Bugler et al. [56].
Instead of a sequential extraction into weak and strong
solvents, the sample is thermally desorbed at two different
temperatures (e.g. 90 8C and 200 8C). The peak areas of
phenoxyethanol obtained at low desorption temperature
Mlow and high desorption temperature Mhigh are used to
calculate a ratio V (corresponding to P in Eq. (3) in Table 4)
(see Table 6).
If the experimental procedure considers only sample 1 and V1
¨
(%) is computed, then the decision criteria were defined by Bugler
et al. [56] as follows (Table 7):
 if V > 10%, ink is fresh. For example, if V > 25%, ink is not older
than two months.
 if V < 10%, no conclusion can be drawn.
¨
Bugler et al. found out that a large number of the inks aged too
fast and therefore no conclusion can be drawn when the ratio V is

Table 6
¨
Procedure to determine the ink age factor (V%) of inks from documents described by Bugler et al. [56].
Method 2

Sample 1 (normal)

Treatment

No treatment

Weak extraction

Extract analysed by GC/MS
Mlow = mass of solvent

Strong extraction

Eq. (3)
Evaluation test

Mlow = mass of solvent
200 8C thermodesorption

Analysis 2
Results 2

After several weeks
90 8C thermodesorption

Analysis 1
Results 1

Sample n = 2, 3, 4 and 5 (naturally aged)
0.5 mm of the ink on paper

Sampling

Extract analysed by GC/MS
Mhigh = mass of solvent
V1 (%) = 100Á[Mlow/(Mlow + Mhigh)]

Mhigh = mass of solvent
Vn (%) = 100Á[Mlow/(Mlow + Mhigh)]
Statistical Neumann’s trend test [69]

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C. Weyermann et al. / Forensic Science International 210 (2011) 52–62

Table 7
Summary of V thresholds values defined in the literature and in conference
proceedings.
Aging
parameter (%)

Threshold
value

Ink entry age

V
V
V

>25%
>10%
<10%

Less than 2 months
Less than 3–4 months
No conclusion

Literature

Aspects of reliability

¨
Bugler et al. [56]
¨
Bugler et al. [64]
¨
Bugler et al. [56]

below 10%. Moreover the authors stated that while according to
their test results, the proposed method for age determination was
applicable to ballpoint inks not older than 1.5 years [55,64]. In
practice, however, the accuracy of the method and the properties
of the inks used in office work limit the measurable time scale to an
ink age of up to 3–4 months [64].
In order to minimize the potential occurrence of false
positive, the authors later considered performing a series of
five analyses every two weeks for a period of two months, while
letting the samples naturally age (these are samples 2–5 in Table
6) [64,68]. The authors also proposed derivatization of phenoxyethanol in order to increase sensitivity and decrease variability[64,68]. The results thus obtained are then used for calculating
a similar aging parameter as the one proposed by Aginsky (D in
Table 4) [33] with the difference that the subsequent samples
are aged naturally instead of artificially. In fact, artificial aging is
faster, but actually still debated largely in the scientific
community and it was not yet demonstrated to reproduce
adequately the natural aging of ink [42]. In this way, using the
V% values of the five samples, each of which is older than the
previously analysed, an aging curve for the questioned ink entry
is obtained. It is then assumed, that a significant drop in the
slope of the curve reflects an ink which is still aging, and that no
significant drop in the curve reflects an ink which is not aging
anymore. From mass screening it was deduced, that aging of
inks can be followed analytically with this method up to 6
months. As a consequence, an ink which is still aging is regarded
as being not older than 6 months. Otherwise no conclusion can
be drawn. The assessment of a ‘‘significant drop’’ in the slope of
the aging curve is performed using the statistical Neumann’s
trend test. The value Q is calculated as follows [69,70]:
Q¼

nÀ1
X
1
ðxi À xiþ1 Þ2
2
ðn À 1Þ Á s i¼1

Table 8
Aspects of reliability for analytical methods. These aspects must be further
evaluated before the application of proposed dating methods in real cases.

(5)

where n is the number of measurements (e.g., n = 5), xi, xi+1, . . . are
the measurements ordered chronologically and s is the standard
deviation. This statistical treatment provides a threshold value
for Q to decide if there is a trend in a series of points given a
selected probability p. The probability level has to be fixed by
the examiner and is generally 95%. For example, a threshold
value of 0.8204 is obtained for n = 5 and p = 95%. If the Q value is
below the threshold value, then the conclusion can be drawn
that the investigated ink is still aging given the selected
probability level.
4. Validation of ink dating methods
The analytical dating methods require a considerable amount of
time and resources. It is therefore important not to underestimate
the task of ensuring their scientific validity before implementing
them in practice [71,72] (Table 8). In forensic ink dating, it is
extremely important not to confound the results of research
experiments performed under laboratory conditions on controlled
samples, with results obtained in real situations on uncontrolled
specimens of limited size, unknown composition and undefined

Short definition

Specificity [73]
LoD, LoQ [38,73]

Ability to detect ink solvents
Limit of reliable measurements
(detection and quantification)
Accuracy
Within laboratory precision
Between laboratory precision
Blind testing on realistic samples

Systematic error [38,73]
Repeatability [73,75]
Reproducibility [73]
Outside proficiency
testing [27,31,33]

storage conditions [41]. Published works present interesting ideas
and promising orientations, but its reporting stage in publications
does not allow yet for a wide application in casework. Stewart and
Fortunato [32] warned that ‘the need to routinely determine the age
of a document appears to have been a driving force in development of
new ink analysis techniques. This could be dangerous, in that the field
may be driven to advance faster than the stage of development of some
of the techniques should allow.’
It is also of particular concern that measurement errors and
irregulars are very rarely mentioned in the literature and are
generally not represented in the figures. It is essential however, to
make certain that predicted differences provoked by aging (under
different influencing factors) are in fact higher than measurement
errors [73]. Furthermore, the ink available in real cases is generally
not sufficient to repeat analysis several time in order to obtain a
mean and a standard deviation. When low quantities are analysed,
such as solvents in ink entries, the detection and quantification
limits (LoD and LoQ, respectively) play an important role in
determining a threshold at which the method is not applicable
anymore [4]. Due to this small sample size and the flowing time, it
is seldom possible to perform ink dating by solvent analysis again
after some time has passed. The most demanding aspect is actually
the inter-laboratory validation. As stated earlier, in the literature
all necessary data are actually required so that any new
technique(s) being proposed can be scrutinized by other experts
in the field [32]. The transparency in forensic science has been often
acknowledged as an essential factor to avoid errors [74,75] and is a
must, in order to develop a methodology in several laboratories.
Often, only final values or given examples (no raw data) are
published in the literature and the reader must accept the
conclusions for granted. This lack of transparency about dating
methods was criticized early in the questioned documents
literature. Stewart and Fortunato wrote in 1996 [32] that ‘If a
technique can be shown to be scientifically sound then the next logical
step would be to conduct independent validation studies at different
laboratories. Before this can occur, however, each technique must be
carefully researched and described so that others can reproduce the
methods and evaluate their effectiveness.’ To that Aginsky answered
as follows [33]: ‘However, this recommendation does not seem
irreproachable. Of course, each method proposed for applying in
casework must be minutely described in a professional journal and
properly scrutinized. But, at the same time, it should be realized that
this natural way related, mainly, to the method presentation,
practically has nothing to do with the method validations, at least,
as for ink dating methods. The matter is that these methods are the
complicated many-staged procedures containing a number of
limitations, ‘‘technological nuances’’ and pitfalls which all are difficult
to exhaustively explain in the article and which may serve as
contributing factors to possible inconsistencies between the procedure,
as it is used by the author(s), and its improper reproductions made by
others who want to evaluate its’ effectiveness or conduct independent
validation study. (. . .) With the above reasons in mind, it becomes
clear why attempts to reproduce similar methods by using their

C. Weyermann et al. / Forensic Science International 210 (2011) 52–62

description, even very detailed, may well lead to confusing results’. If a
method may be reproduced incorrectly by other scientists because
of its difficulty, then the robustness of the method may be
questioned. A robust method would not be significantly affected by
small variations (i.e., error) introduced during the procedure; and
the procedures may be easily exported in other laboratories.
Therefore forensic scientists performing ink dating methods
should contribute actively to the exportation of their method to
other laboratories, thus avoiding misunderstanding leading to
improper reproductions. In fact, to the present date, no two
laboratories that do ink dating via solvent analysis use the same
method, however several laboratories participating in the International Collaboration on Ink Dating (InCID, a subgroup of the
European Document Examiners Working Group) are striving to
harmonize their dating methodologies inspired by the work of
¨
Bugler et al. [56].
Once the validation of the tested methods is carried out
satisfactorily [71,72], blind testing on realistic samples will be
imperative, in order to check the reliability of the method under
real casework conditions. Brunelle and Cantu [27], Margot et al.
[31] and Aginsky [33] agreed on the fact that ‘there is a serious need
for outside proficiency testing of current ink dating methods’. Aginsky
reported having been subjected to outside proficiency testing in
the Division of Identification and Forensic Science of the Israel
Police for method 2 (decrease in extraction efficiency) [33,52,76]. A
document attesting that fact is available on the website of Riley
Welch LaPorte and Associate [76]. According to this document,
Aginsky examined six different ballpoint inks written on different
dates and his results were all correct. The age of the inks at the time
of analyses varied between 1 and 12 months. Five were younger
than 8 months and one was older than 2 months. No indication
about the preparation of samples was detailed (e.g., type and
number of different inks, type of paper, storage conditions). The
number of samples of this testing was very limited and the
conclusion given used only two thresholds (less than 8 months
corresponding to D > 15% and more than 2 months corresponding
to D < 10% [52]). In our opinion, this can by no means serve as a
proof that the method will work on realistic samples (i.e.,
corresponding to uncontrolled conditions encountered in caseworks) and that different threshold values [45] would provide
¨
correct answers. For example, recent studies by Bugler et al. [56]
showed that about half of the investigated inks were ‘fast aging’
and yielded low ratio even when still fresh and thus, a lowerthreshold value cannot be interpreted as coming from an old ink.
Moreover, the time span that can be considered to date inks
through solvent analysis using GC/MS is seriously questioned in
the forensic community. Brunelle and Crawford stated that the ink
dating technology which is based on GC/MS analysis cannot be used
¨
to date inks over six months old [15,46] and Bugler et al.
recommended to analyze ink with a maximum age of 3–4 months
[64]. The feasibility of such dating techniques on ink older than
that must therefore be demonstrated.
Aginsky added that ‘Both techniques (i.e., named here as methods
1 and 2) described have been used numerously in actual cases
involving tax evasion, medical malpractice, altered wills, contractual
disputes, rackets, corruption and organized crime, and many times the
conclusions stated on the basis of the results of the ink dating
examinations (accepted as conclusive by the courts of law in Russia)
directly affected a case [52]’. The fact that acceptance by the courts
is sometimes considered as proof of validation of methods, while
stating that the same methods are probably too delicate to be
reproduced correctly by scientific colleagues should be strongly
questioned. In fact all dating methods should follow complete
validation according the above-mentioned criteria (Table 8) before
their application in court. In conclusion of this Section, Brunelle
and Cantu underlined earlier the ethical responsibilities of forensic

59

scientists performing ink dating examinations [27] by stating that
‘Testimony involving ink dating that does not clearly state the
significance of results obtained and the limitations of what can be
concluded from the results of examination (. . .) would be unethical
according to AAFS (American Academy of Forensic Sciences)
guidelines because it would be misleading.’
5. Ink dating interpretation
Interpretation of ink dating evidence plays an essential role in
the dating process and should not be underestimated in the
development of dating methods [4]. It is very important to consider
all the possible alternative hypotheses for the obtained result to
allow for a balanced interpretation of the evidence
[27,38,74,75,77]. A logical statistical framework based on a
likelihood approach was proposed [38], because it is more correct
than the threshold approach generally reported in the literature. It
has the advantage of taking into account the occurrence of false
positive results which cannot be completely avoided [27],
particularly in a field with many influencing factors that may
introduce additional errors.
For cases where an ink tests as being fresh Aginsky wrote [52]
that ‘If such a result has been obtained for a questioned document
dated, e.g., by over a year preceding the analysis, the examiner can
state with confidence that this document has been backdated.’ One
has to be particularly careful as such a statement is actually
influenced by all the factors mentioned above. In fact, it is not
unconceivable that an ink older than 8 months may in some
circumstances show a ratio D above 12% (for example, an ink
signature on a document placed in a plastic cover with several
other documents also carrying ink entries and stored in a cold,
humid room). Forensic interpretation must therefore take into
account all logical possibilities (i.e., alternative sources for
observed results) and the probability should not be expressed
on the hypotheses (e.g., it is wrong to state the following: ‘it is more
probable that the ink is fresh given the obtained D% ratio’). In order to
formulate a statement in a balanced way, the probability should
actually be formulated on the evidence given two hypotheses (e.g.
‘it is more probable to observe the obtained D% ratio if the ink is fresh
rather than if the ink is old’) [74,75,78]. The likelihood ratio (LR) is
thus defined by the probability of observing a given value of D% if
the ink is of age t1 = A months compared to the probability of
observing the same D% value if the ink was older than A i.e.,
t2 = (A + n) months:
LR ¼

pðDjt 1 Þ
pðDjt 2 Þ

(6)

For example, the evidence can be evaluated given the following
two hypotheses:
 the prosecution states that the ink is 8 months old (t1);
 the defence reports that the ink is 24 months old (t2).
Aginsky [45] reported that the mean value and the standard
deviation for 8 months old blue ink strokes (from 50 different
ballpoint pens) was D = 7.56 Æ 1.13%, while the values for 24 months
old blue ink strokes (from 30 different ballpoint pens) was
D = 1.25 Æ 0.85%. Accepting for simplicity that D values for a given
time tn are normally distributed, the LR can be calculated from the
following equation [79,80]:
LR ¼

f ðDjmt1 ; s 21 Þ
t

f ðDjmt2 ; s 22 Þ
t

(7)

where m is the mean and s2 is the standard deviation of the D%
value. The density of probability for a given value of D = d is

60

C. Weyermann et al. / Forensic Science International 210 (2011) 52–62

60

Table 9
Summary of minimum requirements necessary to reach a sufficient level of
confidence in the development and application of dating methods.

50

Minimum requirements

Log(LR)

30

Purpose

Study of aging kinetics and
influencing factors
Description of methodology

40

Define limit of applicability of
the method
Achieve transparency enabling
reproduction by other laboratories
Reach intra and inter-laboratory reliability
Evaluate probability of evidence given
alternative hypotheses

Validation of methodology
Use of a logical
interpretation model

20
10
0
-10
0

2

4

6

8

10

12

14

16

18

20

D%
Fig. 7. Distribution of likelihood ratio (LR) calculated as a function of the D% values
for the pair of proposition: the ink is 8 months old (t1) and the ink is 24 months old
(t2). Up to a D% of 4, the evidence support the hypothesis t2, while for D ! 5%, the
evidence is more probable given t1.

generally given by the following function [79,80]:
"
#
2
1
ðd À mÞ
f ðDjm; s 2 Þ ¼ pffiffiffiffiffiffiffiffiffiffiffiffi exp À
2s 2
2ps 2

(8)

If a D% value of 5% is obtained for the scenario considered here,
the LR is then written as follows:

LR ¼

f ðDj7:56; 1:13Þ 0:02065
% 188
¼
f ðDj1:25; 0:85Þ 0:00011

This would mean that it is 188 times more likely to observe
D = 5% if the ink is 8 months old (t1) rather than if it is 24 months
old (t2). This calculation can be repeated for all potential values of D
in order to represent a distribution of possible LR for the given pair
of propositions t1 and t2 as a function of D% (Fig. 7).
However, as can be seen both densities of probability are
considerably low and the LR value may change considerably if
another set of propositions were to be compared. Unfortunately,
the necessary data is not available from the literature to test other
scenarios. This logical approach to interpret ink dating evidence
has two main advantages, non negligible for the court: (1) it is
more correct because it takes into account the hypotheses of the
justice and the error rate (false positive occurrence should not be
neglected) and (2) it allows to test all possible scenarios and not
limit the results to values above a certain threshold. Additionally
this approach can be adapted to continuous data and the influence
of several factors on the aging can be introduced in the model to
evaluate their impact on the strength of evidence [79].
6. Conclusion
The drying of ink on paper can to some extent be compared to
the drying of a towel. Thus if the towel was dipped in water or only
used to wipe a wet surface, one takes longer to dry than the other
(i.e., dependence on the initial quantity of solvent). If the towel is
made of cotton or synthetic fabric, again the length of time to dry
will differ (i.e., dependence on the type of substrate) and finally the
time to dry will not be comparable if the towel was kept in a plastic
bag or hung up outside exposed to the sun and wind (i.e.,
dependence on the storage conditions). Also, the evaporation and
diffusion of the ink solvents can be compared to a drop of perfume
on a piece of paper. Over time it evaporates and spreads laterally,

through the paper, and into any paper above and below that may
be in contact with it. This is why, whatever the ink dating method
used may be, the influence of factors such as those mentioned
above must be quantified and taken into account when interpreting the results. At least some reservations should be expressed on
the results if these were not known (Table 9).
Furthermore, ink dating methods should be validated by
determining their limit of quantification, systematic error,
repeatability (within laboratory precision) and reproducibility
(between laboratories precision). For the latter, communication
about the method should be open to allow other laboratories to
reproduce it. This step of harmonisation between laboratories is
not easy, but should not be underestimated. In fact, for a question
as recurrent as the one of documents dating, the necessary
resources should not be an issue for forensic laboratories around
the world. Ideally the technique should then be submitted to blind
testing by an outside qualified laboratory on realistic samples such
as is done in many other forensic disciplines. This is not a small task
because preparing older realistic samples is not straightforward.
However the methods seem to work for ink up to 24 months old at
most. It is therefore feasible.
This last requirement for ink dating methods is an adequate and
logical interpretation model taking into account the methodology’s
error rates, which cannot be neglected in an ethical approach.
Calculations of likelihood ratios should allow for balanced answers
to the court considering both the prosecution and the defence
hypotheses. This will give the justice the necessary information to
consider all information at hand in a global Bayesian framework.
To conclude this article, we wish to quote from Professor
Michael J. Saks’ recent article: ‘‘Forensic identification: From a
faith-based ‘‘Science’’ to a scientific science’’ [81]:
‘‘What can forensic scientists do while waiting for a serious body of
research to evolve that illuminates their particular subfield? The short
answer is: honesty and humility. Confine reports and testimony
within the bounds of the empirically tested findings of the field,
intelligently understood (meaning: not relying excessively on any
single study of a limited aspect of a phenomenon and not
overgeneralizing). If very little is based on empirically tested findings,
simply say so, while stating conclusions in a way that recognizes and
respects the limits of the available knowledge. What one believes or
hopes about a field and what one can know on existing research are
not the same. Refrain from exaggerating what actually is known at
the present stage of the field’s development. Remain within the
bounds of actual knowledge. Abandon claims of uniqueness and
absoluteness. Recognize that forensic identification is a probabilistic
endeavor. Abandon the use of misleading terminology, such as
‘‘match’’ or ‘‘identification’’ or ‘‘scientific certainty.’’ Offer descriptions
and opinions with clarity and candor. Offer conclusions with
modesty, unless and until a body of serious empirically based
knowledge allows more. Resist the culture of exaggeration. Strive for
science-based, not faith-based, forensic science’’.

C. Weyermann et al. / Forensic Science International 210 (2011) 52–62

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Exhibit 28

Declaration of Larry F. Stewart

Exhibit 29

Declaration of Larry F. Stewart

Exhibit 30

Declaration of Larry F. Stewart

Exhibit 31

Declaration of Larry F. Stewart

Exhibit 32

Declaration of Larry F. Stewart

Exhibit 33

Declaration of Larry F. Stewart