ASTM E2228-02

Standard Guide for Microscopic Examination of Textile Fibers

SIGNIFICANCE AND USE
Microscopic examination is one of the least destructive means of determining rapid and accurate microscopic characteristics and generic polymer type of textile fibers. Additionally, a point-by-point, side-by-side microscopic comparison provides the most discriminating method of determining if two or more fibers are consistent with originating from the same source. This guideline requires specific pieces of instrumentation outlined herein.
SCOPE
1.1 This section describes guidelines for microscopical examinations employed in forensic fiber characterization, identification, and comparison. Several types of light microscopes are used including stereobinocular, polarized light, comparison, fluorescence and interference. In certain instances, the scanning electron microscope may yield additional information. Select which test(s) or techniques to use based upon the nature and extent of the fiber evidence.

General Information

• Status: Historical
• Publication Date: 09-Aug-2002
• ICS: 37.020 - Optical equipment
• Technical Committee: E30 - Forensic Sciences
• Drafting Committee: E30.01 - Criminalistics

Relations

• Replaced By: ASTM E2228-10 - Standard Guide for Microscopic Examination of Textile Fibers
• Effective Date: 15-Sep-2010
• Referred By: ASTM E3260-21 - Standard Guide for Forensic Examination and Comparison of Pressure Sensitive Tapes
• Effective Date: 10-Aug-2002
• Referred By: ASTM E2224-23a - Standard Guide for Forensic Analysis of Fibers by Infrared Spectroscopy
• Effective Date: 10-Aug-2002
• Referred By: ASTM E3233-20 - Standard Practice for Forensic Tape Analysis Training Program
• Effective Date: 10-Aug-2002
• Referred By: ASTM E2225-23 - Standard Guide for Forensic Examination of Fabrics and Cordage
• Effective Date: 10-Aug-2002
• Referred By: ASTM E1732-22 - Standard Terminology Relating to Forensic Science
• Effective Date: 10-Aug-2002
• Referred By: ASTM E2227-23e1 - Standard Guide for Forensic Examination of Dyes in Textile Fibers by Thin-Layer Chromatography
• Effective Date: 10-Aug-2002

Standards Content (Sample)

NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
Contact ASTM International (www.astm.org) for the latest information
Designation:E2228–02
Standard Guide for
Microscopic Examination of Textile Fibers
This standard is issued under the fixed designation E2228; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope away from the objective and will move toward the lower
refractiveindexmediumwhenthesampleismovedtowardthe
1.1 This section describes guidelines for microscopical
objective.
examinationsemployedinforensicfibercharacterization,iden-
3.1.5 birefringence—the numerical difference in refractive
tification, and comparison. Several types of light microscopes
indices for a fiber, given by the formula: n{− n'. Birefrin-
are used including stereobinocular, polarized light, compari-
gence can be calculated by determining the retardation (r) and
son, fluorescence and interference. In certain instances, the
thickness (T) at a particular point in a fiber and by using the
scanning electron microscope may yield additional informa-
formula: B= r (nm)/1000T (µm).
tion. Select which test(s) or techniques to use based upon the
3.1.6 comparison microscope—a system of two micro-
nature and extent of the fiber evidence.
scopes positioned side-by-side and connected via an optical
2. Referenced Documents
bridge in which two specimens may be examined simulta-
neously in either transmitted or reflected light.
2.1 ASTM Standards:
3.1.7 compensator—any variety of optical devices that can
D276 Test Methods for Identification of Fibers in Textiles
be placed in the light path of a polarizing microscope to
3. Terminology
introduce fixed or variable retardation comparable with that
exhibitedbythefiber.Theretardationandsignofelongationof
3.1 Definitions of Terms Specific to This Standard:
the fiber may then be determined. Compensators may employ
3.1.1 anisotropic—a characteristic of an object, which has
a fixed mineral plate of constant or varying thickness or a
opticalpropertiesthatdifferaccordingtothedirectioninwhich
mineral plate that may be rotated, or have its thickness varied
lighttravelsthroughtheobjectwhenviewedinpolarizedlight.
by tilting to alter the thickness presented to the optical path
3.1.2 barrier filter—afilterusedinfluorescencemicroscopy
(and retardation introduced) by a set amount.
that suppresses unnecessary excitation light that has not been
3.1.8 compensator, full wave (or red plate)—a compensator
absorbed by the fiber and selectively transmits only light of
usually a plate of gypsum, selenite or quartz, which introduces
greater wavelengths than the cut-off wavelength.
a fixed retardation between 530 to 550 nm (approximately the
3.1.3 Becke line—the bright halo near the boundary of a
retardation of the first order red color on the Michel-Levy
fiber that moves with respect to that boundary as the fiber is
chart).
moved through best focus when the fiber is mounted in a
3.1.9 compensator, quarter wave—a compensator, usually
medium that differs from its refractive index.
withamicaplate,whichintroducesafixedretardationbetween
3.1.4 Becke line method—a method for determining the
125 to 150 nm.
refractiveindexofafiberrelativetoitsmountantbynotingthe
3.1.10 compensator, quartz wedge—a wedge, cut from
direction in which the Becke line moves when the focus is
quartz, having continuously variable retardation extending
changed. The Becke line will always move toward the higher
over several orders of interference colors (usually 3 to 7).
refractive index medium (fiber or mountant when the focal
3.1.11 compensator, Sénarmont—a quarter-wave plate in-
distance is increased and when the focal distance is decreased
serted above the specimen in the parallel “0” position with a
calibrated rotating analyzer. Measures low retardation and
This guide is under the jurisdiction of ASTM Committee E30 on Forensic
requires the use of monochromatic light.
Sciences and is the direct responsibility of Subcommittee E30.01 on Criminalistics.
3.1.12 compensator, tilting (Berek)—a compensator typi-
Current edition approved August 10, 2002. Published October 2002. DOI:
10.1520/E2228-02. callycontainingaplateofcalciteorquartz,whichcanbetilted
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
bymeansofacalibrateddrumtointroducevariableretardation
contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
up to about ten orders.
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
E2228–02
3.1.13 cortex—the main structural component of hair con- 3.1.27 lignin—the majority non-carbohydrate portion of
sisting of elongated and fusiform (spindle-shaped) cells. The wood. It is an amorphous polymeric substance that cements
cellulosic fibers together. The principal constituents of woody
cortex may contain pigment grains, air spaces called cortical
fusi, and structures called ovoid bodies. cell walls.
3.1.28 lumen—the cavity or central canal present in many
3.1.14 crimp—the waviness of a fiber.
natural fibers (for example, cotton, flax, ramie, jute, hemp). Its
3.1.15 crossover marks—oblique flattened areas along silk
presence and structure are often useful aids in identification.
fibers caused by the overlapping of extruded silk fibers before
3.1.29 luster—the gloss or shine possessed by a fiber,
they have dried completely.
resultingfromitsreflectionoflight.Thelusterofmanufactured
3.1.16 cuticle—the layer of scales composing the outer
fibers is often modified by use of a delustering pigment.
surface of a hair shaft. Cuticular scales are normally classified
3.1.30 manufactured fiber—a class name for various fami-
into three basic types: coronal (crown-like), spinous (petal-
lies of fibers produced from fiber-forming substances, which
like), and imbricate (flattened).
may be synthesized polymers, modified or transformed natural
3.1.17 delustrant—a pigment, usually titanium dioxide,
polymers and glass.
used to dull the luster of a manufactured fiber.
3.1.31 medulla—thecentralportionofahaircomposedofa
3.1.18 dichroism—the property of exhibiting different col-
seriesofdiscretecellsoranamorphousspongymass.Itmaybe
ors, especially two different colors, when viewed along differ-
air-filled, and if so, will appear opaque or black using trans-
ent axes by plane polarized light.
mitted light or white using reflected light. In animal hair,
severaltypeshavebeendefined:uniserialormultiserialladder,
3.1.19 dislocations—distinct features that occur in natural
cellular or vacuolated, and lattice.
fibers(forexample,flax,ramie,jute,hemp)intheshapeofX’s,
3.1.32 Michel-Lévy chart—a chart relating thickness, bire-
I’s, and V’s that are present along the fiber cell wall. These
fringence,andretardationsothatanyoneofthesevariablescan
features are often useful for identification.
be determined for an anisotropic fiber when the other two are
3.1.20 dispersion of birefringence—the variation of bire-
known.
fringence with wavelength of light. When dispersion of bire-
3.1.33 microscopical—concerning a microscope or the use
fringence is significant in a particular fiber, anomalous inter-
of a microscope.
ference colors not appearing in the regular color sequence of
3.1.34 modification ratio—a geometrical parameter used in
the Michel-Levy chart may result. Strong dispersion of bire-
the characterization of noncircular fiber cross-sections. The
fringencemayalsointerferewiththeaccuratedeterminationof
modification ratio is the ratio in size between the outside
retardation in highly birefringent fibers.
diameter of the fiber and the diameter of the core. It may also
3.1.21 dispersion staining—atechniqueforrefractiveindex
be called “aspect ratio.”
determination that employs central or annular stops placed in
3.1.35 natural fibers—a class name of fibers of plant origin
the objective back focal plane of a microscope. Using an
(for example, cotton, flax, ramie), animal origin (for example,
annular stop with the substage iris closed, a fiber mounted in a
silk, wool, and specialty furs) or of mineral origin (for
high dispersion medium will show a colored boundary of a
example, asbestos).
wavelengthwherethefiberandthemediummatchinrefractive
3.1.36 pigment—a finely divided insoluble material used to
index. Using a central stop, the fiber will show colors compli-
deluster or color fibers (for example, titanium dioxide, iron
mentary to those seen with an annular stop.
oxide).
3.1.22 dye—soluble substances that add color to textiles.
3.1.37 plane polarized light—light that is vibrating in one
Dyes are classified into groups that have similar chemical
plane.
characteristics (for example, aniline, acid, and azo). They are
3.1.38 pleochroism—the property of exhibiting different
incorporated into the fiber by chemical reaction, absorption, or
colors, especially three different colors, when viewed along
dispersion.
different axes by plane polarized light.
3.1.23 excitation filter—afilterusedinfluorescencemicros-
3.1.39 polarized light—a bundle of light rays with a single
copy that transmits specific bands or wavelengths of energy
propagation direction and a single vibration direction. The
capable of inducing visible fluorescence in various substrates.
vibration direction is always perpendicular to the propagation
3.1.24 inorganic fibers—a class of fibers of natural mineral
direction. It is produced by use of a polarizing filter, from
origin(forexample,chrysotileasbestos)andmanmademineral
ordinary light by reflection, or double refraction in a suitable
origin (for example, fiberglass).
pleochroic substance.
3.1.25 interference colors—colors produced by the interfer-
3.1.40 polarized light microscope—a microscope equipped
ence of two out-of-phase rays of white light when a birefrin-
with two polarizing filters, one below the stage (the polarizer)
gent material is observed at a non-extinction position between
and one above the stage (the analyzer).
crossed polars. The retardation at a particular point in a
3.1.41 privileged direction (of a polarizer)—thedirectionof
birefringent fiber may be determined by comparing the ob-
vibration to which light emerging from a polarizer has been
served interference color to the Michel-Lévy chart.
restricted.
3.1.26 isotropic—a characteristic of an object in which the 3.1.42 refractive index—foratransparentmedium,adimen-
optical properties remain constant irrespective of the direction sionless number that is the ratio of the velocity of light in a
of propagation or vibration of the light through the object. vacuum to the velocity of light in that medium.
E2228–02
3.1.43 relative refractive index—the estimate of the refrac- may also be employed. Other methods such as tape lifting or
tive index of a fiber in relation to the index of its surrounding gentle scraping are usually conducted after a visual examina-
medium. tion. Tape lifts should be placed on clear plastic sheets, glass
3.1.44 retardation (r)—the actual distance of one of the microscope slides, or another uncontaminated substrate that
doubly refracted rays behind the other as they emerge from an eases the search and removal of selected fibers. Tapes should
anisotropic fiber. Dependent upon the difference in the two not be over loaded. The tape lifts or any material recovered
refractive indices, n{− n', and the thickness of the fiber. from scraping should be examined with a stereomicroscope
3.1.45 sign of elongation—a property of fibers referring to and fibers of interest isolated for further analysis. Fibers on
the elongation of a fiber in relation to refractive indices. If tape lifts may be removed using tweezers, other microscopic
elongatedinthedirectionofthehighrefractiveindex,thefiber tools and solvents (1-6). Tape should not be attached to paper
is said to be positive; if elongated in the direction of the low or cardboard.
refractive index, it is said to be negative. 6.2 Care should be taken to ensure contamination does not
3.1.46 spherulites—spherescomposedofneedlesorrodsall occur. This must be accomplished by examining questioned
oriented perpendicular to the outer surface, or a plane section and known items in separate areas and/or at different times.
through such a sphere. A common form of polymer crystalli- The work area and tools must be thoroughly cleaned and
zation from melts or concentrated solutions. inspected before examining items that are to be compared.
3.1.47 stereomicroscope—a microscope containing two
7. Analysis
separate optical systems, one for each eye, giving a stereo-
scopic view of a specimen.
7.1 Fibers should be first examined with a stereomicro-
3.1.48 surface dye—a colorant bound to the surface of a
scope. Physical features such as crimp, length, color, relative
fiber.
diameter, luster, apparent cross section, damage, and adhering
3.1.49 synthetic fibers—a class of manufactured polymeric
debris should be noted. Fibers may then be tentatively classi-
fibers, which are synthesized from chemical compounds (for
fied into broad groups such as synthetic, natural, or inorganic.
example, nylon, polyester).
If the sample contains yarns, threads, or sections of fabric,
3.1.50 technical fiber—a bundle of natural fibers composed
construction should be recorded (7-9).
of individual elongated cells that can be physically or chemi-
7.1.1 If all of the physical characteristics appear the same
cally separated and examined microscopically for identifying
under the stereoscope, an examination of the fibers with a
characteristics (for example, hemp, jute, and sisal).
comparison microscope should be conducted. This side-by-
3.1.51 thermoplastic fiber—asyntheticfiberthatwillsoften
side, point-by-point examination is a valuable technique to
or melt at high temperatures and harden again when cooled.
discriminate between fibers, especially those that may appear
3.1.52 ultimates—individual fibers from a technical fiber
tobesimilar.Thephysicalcharacteristicsofthefibers(see7.3)
(see 3.1.50).
must be compared visually with the comparison microscope to
determine if they are the same in the known and questioned
4. Significance and Use
samples. Photography is recommended to capture the salient
features for later demonstration.
4.1 Microscopic examination is one of the least destructive
7.1.2 Comparisons should be made using a properly cali-
means of determining rapid and accurate microscopic charac-
brated and aligned microscope under the same illumination
teristics and generic polymer type of textile fibers. Addition-
conditions at the same magnifications. For comparison micro-
ally, a point-by-point, side-by-side
...