ASTM E1422-98
(Guide)Standard Guide for Test Methods for Forensic Writing Ink Comparison
Standard Guide for Test Methods for Forensic Writing Ink Comparison
SCOPE
1.1 This Guide is intended to assist forensic examiners comparing writing or marking inks. Included in this analysis scheme are the necessary tools and techniques available to reach conclusions as to the common or different origin of two samples of ink.
1.2 Identifying ink formulas as to their manufacturer or time of manufacture as well as performing ink dating examinations are beyond the scope of this guide.
1.3 This standard does not purport to address all of the safety problems, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
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Standards Content (Sample)
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Designation: E 1422 – 98
Standard Guide for
Test Methods for Forensic Writing Ink Comparison
This standard is issued under the fixed designation E 1422; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (e) indicates an editorial change since the last revision or reapproval.
INTRODUCTION
This guide is intended to be a general guide for forensic ink examinations, both for the experienced
document examiner (E 444) and for those unfamiliar with previously reported procedures. The aim is
to include those techniques that will provide the most information about an ink with the least damage
to the document. Therefore, this guide refers to well-reported and thoroughly tested techniques
currently in use by document examiners in general practice and dedicated forensic ink comparison
facilities.
By following the procedures outlined here, an examiner can accurately discriminate ink formulas
and reduce the possibility of false matches of ink samples from different sources or incorrect
differentiation of ink samples with a common origin.
1. Scope NBS Standard Sample No. 2106 ISCC-NBS Centroid Color
Charts
1.1 This Guide is intended to assist forensic examiners
NBS Special Pub. 440 Color: Universal Language and
comparing writing or marking inks. Included in this analysis
Dictionary of Names
scheme are the necessary tools and techniques available to
reach conclusions as to the common or different origin of two
3. Terminology
samples of ink.
3.1 Definitions:
1.2 Identifying ink formulas as to their manufacturer or time
3.1.1 chromatography—a method of separating substances
of manufacture as well as performing ink dating examinations
that is widely used in analytical and preparative chemistry. It
are beyond the scope of this guide.
involves the flow of a liquid or gas mobile phase over a solid
1.3 This standard does not purport to address all of the
or liquid stationary phase. As the mobile phase flows past the
safety concerns, if any, associated with its use. It is the
stationary phase, a solute will undergo repeated adsorption and
responsibility of the user of this standard to establish appro-
desorption and move along at a rate depending, among other
priate safety and health practices and determine the applica-
factors, on its ratio of distribution between two phases. If their
bility of regulatory limitations prior to use.
distribution ratios are sufficiently different, components of a
2. Referenced Documents mixture will migrate at different rates and produce a charac-
teristic pattern (chromatogram).
2.1 ASTM Standards:
3.1.2 fluorescence—a process by which radiant flux of
D 1535 Test Method of Specifying Color by the Munsell
certain wavelengths is absorbed and reradiated nonthermally at
System
other, usually longer, wavelengths. (E 284)
E 131 Terminology Relating to Molecular Spectroscopy
3.1.3 infrared (IR)—referring to radiant flux having wave-
E 284 Terminology of Appearance
lengths longer than the wavelengths of light, usually wave-
E 444 Guide for Descriptions of Scopes of Work Relating to
lengths from about 760 nm to about 3 mm. (E 284)
Forensic Sciences for Questioned Document Area
3.1.4 light—electromagnetic radiant energy that is visually
2.2 NIST Standards:
detectable by the normal human observer, radiant energy
having wavelengths from about 380 nm to about 780 nm.
(E 284)
This guide is under the jurisdiction of ASTM Committee E-30 on Forensic 3.1.5 luminescence—the emission of radiant energy during
Sciences and is the direct responsibility of Subcommittee E30.02 on Questioned
a transition from an excited electronic state of an atom,
Documents.
molecule or ion to a lower electronic state. (E 131)
Current edition approved Jan. 10, 1998. Published December 1998. Originally
published as E 1422 – 91. Last previous edition E 1422 – 97.
Annual Book of ASTM Standards, Vol 06.01.
Annual Book of ASTM Standards, Vol 03.06.
4 Available from U.S. Department of Commerce, National Bureau of Standard
Annual Book of ASTM Standards, Vol 14.02.
Reference Materials, R. B311, Chemistry Building, Gaithersburg, MD 20899.
Copyright © ASTM, 100 Barr Harbor Drive, West Conshohocken, PA 19428-2959, United States.
E 1422
3.1.6 metamers—specimens differing in spectral reflectance basic categories of question: (1) whether an ink is the same (in
but having colors that match in light of one spectral composi- formula) as that on other parts of the same document or on
tion, when viewed by one observer, but may not match in light other documents; (2) whether two writings with similar ink
of other spectral compositions, or when viewed by another have a common origin, that is, the same writing instrument or
observer. (E 284) ink well; (3) whether the ink of entries dated over a period of
3.1.7 spectroscopy—in the most general sense spectroscopy time is consistent with that dating or indicates preparation at
is the study of the absorption or emission of electromagnetic one time; (4) whether ink is as old as it purports to be (1).
energy by a chemical species as a function of the energy 4.2 The procedures set forth in this guide are directly
incident upon that species. applicable to giving a full answer to only the first of these four
3.1.8 source—an object that produces light or other radiant questions.
flux. (E 284) 4.3 With regard to the second question, differentiation of
3.1.9 ultraviolet (UV)—referring to radiant flux having formula (question one) would indicate a negative answer to this
wavelengths shorter than the wavelengths of light, usually question, as would differentiation with any of the additional
wavelengths from about 10 nm to 380 nm. methods listed in Section 3. When dealing with contemporary
3.1.9.1 Discussion—Long-wave UV usually refers to the inks, however, a match of ink samples involving agreement in
spectral range of UV-A, with wavelengths from about 315 nm all observable aspects of all the techniques considered in this
to 380 nm. Short wave UV usually refers to the spectral range guide, while consistent with common origin, would not be
of UV-C, with wavelengths from about 100 nm to 280 nm. sufficient to support a definite opinion of common origin (2).
3.2 Definitions of Terms Specific to This Standard: Contemporary ink rarely has sufficient individuality to support
3.2.1 ballpoint pen ink—writing or marking media intended a determination of common origin at less than the manufac-
for use in a ball point pen. Typically, a thick, high viscosity ink turing batch level.
with an oil, glycol or rubber base.
NOTE 1—Contemporary mass-produced inks are usually distributed as
3.2.2 dichroic filter—a filter with two transmission bands.
a component in a complete writing instrument or in a cartridge. With such
These bands are usually widely separated, and can be of
packaging the ink is not subject to the mixing of inks and exposure to
significantly different size. environmental contamination that could individualize ink from a given ink
well at a specific point in time (1, 3). This sort of analysis, potentially
3.2.3 gel pen ink—writing or marking media intended for
useful in the examination of older documents or those prepared under
use in a “gel-type” roller pen. Gel pen inks constitute a unique
certain circumstances, is beyond the scope of this guide, as is examination
class of non-ballpoint pen inks. Typically, an aqueous ink of
of the ink line to individualize the writing instrument that produced it
high viscosity, capable of maintaining a stable dispersed or
based on its performance characteristics.
dissolved state of the coloring material even after a prolonged
4.4 As to the third and fourth questions involving the age of
period and exhibiting high fluidity under a shearing force. The
ink, dating techniques for determining either the relative age of
ink contains a coloring material (pigment or dyes), acid-
ink samples (from the same or different documents) or the
modified heteropolysaccharide and aqueous medium (water
absolute amount of time since the writing of an ink line are also
and water-soluble organic solvent), in which water constitutes
beyond the scope of this guide.
at least 50 % by weight. Due to the incorporation of pigments
4.5 However, regarding question three, it may be of great
into these formulations, the procedures outlined in this guide
importance in a forensic situation involving writing dated over
for TLC evaluations will be of limited value.
a period of time to determine that one or more than one ink
3.2.4 infrared luminescence (IRL)—the emission of radiant
formula is present, that the use of various ink formulas fits a
energy during a transition from an excited electronic state of an
pattern, that a particular ink formula matches samples of a
atom, molecule or ion to a lower electronic state (fluorescence
known date, etc.
or phosphorescence, or both), where the spectrum of the
4.6 As to the last question, a limit as to the possible age of
excitation source is in the ultraviolet (UV) or visible region of
an ink entry can be inferred by establishing the date of first
the electromagnetic spectrum, or both, and the spectrum of the
production of the ink formula. Although beyond the scope of
emitted energy is in the far red or infrared (IR) region of the
this guide, identifying ink formulas as to their manufacturer or
electromagnetic spectrum.
time of manufacture utilizes many of the analytical procedures
3.2.5 ink formula—a precise recipe or set of ingredients and
described here. Specialized knowledge and experience on the
their quantities that the manufacturer specifies for the final ink
part of the examiner, as well as access to a collection or library
product. These ingredients are colorants (dyes and pigments)
of ink reference samples is also required.
and vehicle components (volatile solvents, resins, etc.).
4.6.1 Such an ink library consists of samples of ink formulas
3.2.6 match between ink samples—the inability to distin-
from known sources, usually manufacturers of ink, or writing
guish between ink samples at a given level of analysis.
or marking instruments, or a combination thereof. The ink
3.2.7 non-ballpoint pen ink—writing or marking media
reference samples are usually cataloged, analyzed, and stored
intended for use in a writing or marking instrument other than
according to the methods described in Refs (2, 4, 5 and 6).
a ballpoint pen, including a dip or fountain pen, porous point
Even with access to a comprehensive collection, association of
pen, roller pen, marking instrument, etc. Typically, a thin, low
an unknown ink sample with a single known formula is not
viscosity ink with a water or solvent base.
4. Significance and Use
The boldface numbers in parenthesis refer to the list of references at the end of
4.1 Ink comparisons are usually performed to answer four this guide.
E 1422
always possible. This is because some ink formulas are not 6.4 Reagents for Thin Layer Chromatography (TLC) Devel-
distinguishable, however, in most cases the analytical proce- oping Solvents:
dures outlined here are sufficiently discriminating that formulas 6.4.1 Solvent System I— Ethyl acetate, ethanol, water
are distinguishable. (70 + 35 + 30).
4.7 Comparison of ink samples by analysts without an ink 6.4.2 Solvent System II—N-butanol, ethanol, water
library can still provide valuable information. However, added (50 + 10 + 15).
significance can be given to the meaning of a match if the 6.5 Other ink extracting solvents and developing solvents in
relative rarity or commonness of the ink formula is known. accordance with Refs (5, 6, and 10).
Familiarity with or access to a comprehensive reference 6.6 Equipment for Optical Examinations:
collection of inks is useful for this purpose. 6.6.1 Stereomicroscope:
4.8 In expressing conclusions it should be remembered that
NOTE 3—Five to one hundred power total magnification is a range that
a match indicates that the ink samples are of the same formula
has been found useful.
or of two similar formulas with the same nonvolatile compo-
6.6.2 UV Lamps or View Box, with both long-wave UV and
nents. The possibility that other analytical techniques might be
short-wave UV lamps.
able to differentiate them should always be considered (2).
6.6.3 Colored Filters, (gelatin, colored glass, interference
4.8.1 Therefore, conclusions in this situation should never
filters) as needed for visual and photographic differentiation of
indicate that two ink samples are “identical” or “the same ink,”
inks.
but must be limited to statements indicating “inability to
6.6.4 Dichroic Filters, See Ref (11).
distinguish the ink samples at this level of analysis” or
6.6.5 Photographic equipment with appropriate film, light-
“exhaustive chemical and physical testing failed to detect any
ing, and filters for differentiation of ink samples.
differences between the ink samples” (2).
6.6.6 Photographic equipment with appropriate film, light-
ing, and filters for recording reflected infrared (RIR) and
5. Interferences
infrared luminescence (IRL).
5.1 Most interferences with ink examinations come from
6.6.7 IR image conversion device or system with appropri-
variables that interact with the ink. These can be part of the
ate light sources and filters for use in RIR and IRL modes as
writing process, such as blotting wet ink (1, 2), or variations in
well as appropriate photographic equipment, computer hard-
the paper (7), or various forms of contamination on the
ware and software for image acquisition or processing, or both.
document (7, 8), or a combination thereof. Simple precautions
6.6.8 Barrier Filters for RIR and IRL—Long pass filters,
can usually avoid problems.
preferably sharp cut, that block visible flux. Suitable gelatin,
5.2 Note and record any differences in the substrate, such as
colored glass, and interference filters are commercially avail-
the use of different paper for different documents or pages of a
able (12, 13, 14).
multipage document. Also note and record variations in the
NOTE 4—Since ink reactions can vary, it is advisable to use a series of
document, such as a signature written over a photograph on an
filters with cut on wavelengths from the red through the IR range of the
identity document, multicolored paper with different dyes or
film or detector.
colors of underprinting, intersections with printed or typed
6.6.9 Excitation Source for IRL—Sources include: a con-
material, etc. (7, 8).
tinuous spectrum lamp with a filter to eliminate flux in the IR
5.3 The results of prior handling or testing should also be
and far red region of the spectrum, for e
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