July 1999 Volume 1 Number
This document is intended
to be a suggested revision to the original ASTM E1610-94 Guide.
This revision is the product of the Paint Subgroup of the Scientific
Working Group for Materials Analysis (SWGMAT). Its ultimate acceptance
as an ASTM
document will be the responsibility of ASTM Committee E-30 on
Forensic Sciences. You are invited to submit constructive feedback
on the Document Comments Form.
1.1. Forensic paint analyses
and comparisons are typically distinguished by sample size that
precludes the application of many standard industrial paint analysis
procedures or protocols. The forensic paint examiner must address
concerns such as the issues of a case or investigation, sample
size, complexity and condition, environmental effects, and collection
methods. These factors require that the forensic paint examiner
must choose test methods, sample preparation schemes, test sequence,
and degree of sample alteration and consumption suitable to each
1.2. This document is an
introduction for the forensic examination of paints and coatings.
It is intended to assist personnel who conduct forensic paint
analyses in the evaluation, selection, and application of tests
that may be of value to the investigation. The guidelines that
follow describe methods to develop discriminatory information
using an efficient and reasonable order of testing. The need
for validated methods and quality assurance guidelines is also
addressed. This document is not intended to be a detailed methods
description or rigid scheme for the analysis and comparison of
paints but a guide to the strengths and limitations of each analytical
method. The goal is to provide a consistent approach to forensic
1.3. Some of the methods
discussed in these guidelines involve the use of dangerous chemicals,
temperatures, and radiation sources. This document does not address
the possible safety hazards or precautions associated with its
application. It is the responsibility of the user of these guidelines
to establish appropriate safety and health practices and to determine
the applicability of regulatory limitations prior to use.
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2.1. ASTM D16 Terminology
Relating to Paint, Varnish, Lacquer, and Related Products1
2.2. ASTM D1535 Method for
Specifying Color by Munsell System
2.3. ASTM E308 Test Method
for Computing the Colors of Objects by Using the CIE System
2.4. ASTM E1492 Practice
for Receiving, Documenting, Storing, and Retrieving Evidence
in a Forensic Science Laboratory2
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3.1. For definitions of terms
used in these guidelines other than those listed, see ASTM D16
Terminology Relating to Paint, Varnish, Lacquer, and Related
3.2. Descriptions of Terms
Specific to this Guide:
3.2.1. Binder: A nonvolatile
portion of the liquid vehicle of a coating, which serves to bind
or cement the pigment particles together.
3.2.2. Coating: A generic
term for paint, lacquer, enamel, or other liquid or liquefiable
material that is converted to a solid, protective, or decorative
film or a combination of these types of films after application.
3.2.3. Discriminate: To distinguish
between two samples on the basis of significant differences;
3.2.4. Discriminating Power:
The ability of an analytical procedure to distinguish between
two items of different origin.
3.2.5. Known Sample: A coating
sample of established origin.
3.2.6. Paint: Commonly known
as a pigmented coating.
3.2.7. Pigment: A finely
ground, inorganic or organic, insoluble, and dispersed particle.
Besides color, a pigment may provide many of the essential properties
of paint such as opacity, hardness, durability, and corrosion
resistance. The term pigment includes extenders.
3.2.8. Questioned Sample:
A coating sample whose original source is unknown.
3.2.9. Significant Difference:
A difference between two samples that indicates that the two
samples do not have a common origin.
3.2.10. Additive (modifier):
Any substance added in a small quantity to improve properties.
Additives may include substances such as driers, corrosion inhibitors,
catalysts, ultraviolet absorbers, and plasticizers.
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4.0. Quality Assurance Considerations
4.1. A quality assurance
program must ensure that analytical testing procedures and reporting
of results are monitored by proficiency tests and technical audits.
General quality assurance guidelines may be found in Trace Evidence
Quality Assurance Guidelines (1).
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Summary of Practice
5.1. Physical and Chemical
Paint films are characterized by a number of physical and chemical
features. The physical characteristics may include color, layer
sequence and thickness, surface and layer features, contaminants,
and weathering. Chemical components may include pigments, polymers,
and additives. These features can be determined and evaluated
by a variety of macroscopical, microscopical, chemical, and instrumental
methods. Limited sample size and sample preservation requirements
mandate that these methods be selected and applied in a reasonable
sequence to maximize the discriminating power of the analytical
5.2. Questioned and Known
Searching for differences between questioned and known samples
is the basic thrust of forensic paint analysis and comparison.
However, differences in appearance, layer sequence, size, shape,
thickness, or some other physical or chemical feature can exist
even in samples known to be from the same source. A forensic
paint examiner's goal is to assess the significance of any observed
differences. The absence of significant differences at the conclusion
of an analysis suggests that the paint samples could have a common
origin. The strength of such an interpretation is a function
of either or both the type or number of corresponding features.
5.3. Motor Vehicle Identification
An important aspect of forensic paint analysis is the identification
of the possible makes, models, and years of manufacture of motor
vehicles from paint collected at the scene of a crime or an accident.
The color comparison and chemical analysis of the undercoat and
topcoat systems requires a knowledge of paint formulations and
processes, collections of paint standards, and databases of color
and composition information.
5.4. Sample Documentation
The test procedure
selected in a paint analysis and comparison begins with thorough
sample documentation. Some features of that documentation are
described in ASTM E1492 Practice for Receiving, Documenting,
Storing, and Retrieving Evidence in a Forensic Science Laboratory.2
Analysis generally begins with appropriate nondestructive tests.
If the initial tests are inconclusive or not exclusionary, the
examination may proceed with additional tests that are selected
on the basis of their potential for use in evaluating or discriminating
the samples of interest or both.
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Significance and Use
6.1. These guidelines are
designed to assist the forensic paint examiner in selecting and
organizing an analytical scheme for identifying and comparing
paints and coatings. The size and condition of the sample or
samples will influence the selected analytical scheme.
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7.0. Collection of Suitable Samples
7.1. The potential for physical
matches between known and questioned samples must be considered
before selecting the method of paint sample collection. Care
should be taken to preserve the potential for a physical match.
7.2. Questioned Samples
7.2.1. Questioned samples should include all loose or transferred
paint materials. Sources of questioned samples can include tools,
floors, walls, glass fragments, hair, fingernails, roadways,
adjacent structures, transfers or smears on vehicles, or transfers
to or from individuals such as damaged fabric with paint inclusions.
Items with paint transfers should be appropriately packaged and
submitted in their entirety for examination whenever possible.
If sampling is necessary, the procedures listed in Trace Evidence
Recovery Guidelines (2) may be used. When paint evidence is recognized,
every effort should be made to manually remove it before using
tape lifts to collect other types of evidence. If paint is collected
with tape lifts, be aware of the possible difficulty encountered
when attempting to manipulate paint samples bearing adhesive
residues. In addition, components of the adhesive could contaminate
the paint sample and change its apparent chemistry.
7.2.2. Smeared transfers
can exhibit mingling of components from several layers or films
that could preclude application of some of the analytical methods
discussed in these guidelines. Because of the difficulties associated
with collecting smeared or abraded samples, the entire object
bearing the questioned paint should be submitted to the laboratory
7.2.3. When contact between
two coated surfaces is indicated, the possibility of cross transfers
must be considered. Therefore, if available, samples from both
surfaces should be collected.
7.3. Known Samples
7.3.1. When feasible, known paint samples must be collected from
areas as close as possible to, but not within, the point or points
of damage or transfer. These damaged areas are usually not suitable
sources of known samples. The collected known samples should
contain all layers of the undamaged paint film. Substantial variations
in thickness and layer sequences over short distances can exist
across a painted surface. This is particularly true in architectural
paint and automotive films where the curves, corners, and edges
are often impact points and may have been subjected to previous
damage, sanding, or overpainting. If necessary, several known
paint samples should be taken to represent all damaged areas.
Known paint samples collected from different areas should be
packaged separately and labeled appropriately.
7.3.2. The surface underlying
the suspected transfer area should be included for analysis when
possible. Adjacent sections removed from a wall, ceiling, door,
window, implement handle, and automobile door, fender, and hood
are examples of items that can be valuable for assessing questioned
and known sample differences and for evaluating the possible
cross transfer of trace materials.
7.3.3. Paint flakes can be
removed from the parent surface by a number of methods. These
include but are not limited to the following: lifting or prying
loosely attached flakes, cutting samples of the entire paint
layer structure using a clean knife or blade, or dislodging by
gently impacting the opposite side of the painted surface. When
cutting, it is important that the blade be inserted down to the
parent surface. It should be noted that no one method of sampling
should be relied upon exclusively.
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Part 2 (Section 8.0)
Part 3 (Sections 9.0-11.0)
You are invited to
submit constructive feedback on the Document
FORENSIC SCIENCE COMMUNICATIONS JULY 1999 VOLUME 1 NUMBER 2