ASTM E2539-14(2021)

This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
Designation: E2539 − 14 (Reapproved 2021)
Standard Test Method for
Multiangle Color Measurement of Interference Pigments
This standard is issued under the fixed designation E2539; 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.
INTRODUCTION
Objects that exhibit a change in color with different angles of illumination and view are said to be
“gonioapparent.” The tristimulus colorimetric values of gonioapparent objects are derived using the
spectral reflectance factors obtained from spectrometric measurements or colorimetric measurements
atvariousanglesofilluminationanddetection.Thetristimuluscolorimetricvaluesarecomputedusing
the spectral reflectance factors of the object, the CIE Standard Observer, and the spectral power
distribution of the illuminant, as described in Practice E308. This Test Method, E2539, specifies the
color measurement of interference pigments at various illumination and detection angles.
1. Scope 1.6 Interference pigments are typically evaluated for color
and color appearance in a medium, such as paint or ink. The
1.1 This test method covers the instrumental requirements
gonioapparent effect depends strongly on the physical and
and required parameters needed to make instrumental color
chemical properties of the medium. Some of the properties
measurements of thin film interference pigments. This test
affecting color and color appearance include vehicle viscosity,
methodisdesignedtoencompassinterferencepigmentsusedin
thickness, transparency, and volume solids. As a general rule,
architectural applications, automobiles, coatings, cosmetics,
for quality control purposes, interference pigments are best
inks, packaging, paints, plastics, printing, security, and other
evaluated in a masstone product form. In some cases this
applications.
product form may be the final product form, or more typically
1.2 Characterization of the optical behavior of materials
a qualified simulation of the intended product form (such as a
colored with interference pigments requires measurement at
paint drawdown) that in terms of color and appearance
multiple angles of illumination and detection.
correlates to final product application.
1.3 Datatakenutilizingthistestmethodarequantitativeand
1.7 This standard does not address the requirements for
are appropriate for quality control of interference pigment
characterizingmaterialscontainingmetalflakepigments.Mea-
color.
surements of the optical characteristics of materials containing
metal flake pigments are described in Test Method E2194.
1.4 The measurement results are usually expressed as re-
flectance factors, tristimulus color values, or as CIE L*a*b*
1.8 The values stated in SI units are to be regarded as the
color coordinates and color difference.
standard. The values given in parentheses are for information
1.5 The totality of data taken may not be necessary for only.
evaluatingmixturesalsocontainingnon-interferencepigments.
1.9 This standard does not purport to address all of the
The committee is investigating and evaluating the appropriate-
safety concerns, if any, associated with its use. It is the
ness of this test method for those materials. It is the responsi-
responsibility of the user of this standard to establish appro-
bility of the users to determine the applicability of this test
priate safety, health, and environmental practices and deter-
method for their specific applications.
mine the applicability of regulatory limitations prior to use.
1.10 This international standard was developed in accor-
dance with internationally recognized principles on standard-
This test method is under the jurisdiction of ASTM Committee E12 on Color
and Appearance and is the direct responsibility of Subcommittee E12.12 on
ization established in the Decision on Principles for the
Gonioapparent Color.
Development of International Standards, Guides and Recom-
Current edition approved June 1, 2021. Published June 2021. Originally
mendations issued by the World Trade Organization Technical
approved in 2008. Last previous edition approved in 2017 as E2539–14 (2017).
DOI: 10.1520/E2539-14R21. Barriers to Trade (TBT) Committee.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
E2539 − 14 (2021)
2. Referenced Documents 5.2 These data can be used for acceptance testing, design
2 purposes, research, manufacturing control, and quality control.
2.1 ASTM Standards:
E284Terminology of Appearance
5.3 Specimensmustbestatisticallyrepresentativeoftheend
E308PracticeforComputingtheColorsofObjectsbyUsing
use.
the CIE System
5.4 Applicability of this test method for other materials,
E805Practice for Identification of Instrumental Methods of
includingcombininginterferencepigmentswithabsorbingand
Color or Color-Difference Measurement of Materials
scattering pigments should be confirmed by the user.
E1164PracticeforObtainingSpectrometricDataforObject-
Color Evaluation
6. Environmental Conditions
E1345Practice for Reducing the Effect of Variability of
Color Measurement by Use of Multiple Measurements
6.1 If the standard laboratory conditions listed below
E1708Practice for Electronic Interchange of Color and
change during the test or from test to test by an appreciable
Appearance Data
amount,theseconditionsmayreduceaccuracyandprecisionof
E1767Practice for Specifying the Geometries of Observa-
this test method. In some cases these effects may only be
tion and Measurement to Characterize the Appearance of
observed during the performance of the test.
Materials
6.2 Factors Affecting Test Results—The following factors
E2194Test Method for Multiangle Color Measurement of
are known to affect the test results.
Metal Flake Pigmented Materials
6.2.1 Extraneous Radiation—Light from sources other than
E2480Practice for Conducting an Interlaboratory Study to
theilluminator(s)andanynear-infrared(NIR)mustbeshielded
Determine the Precision of a Test Method with Multi-
from entering the test apparatus.
Valued Measurands
6.2.2 Vibrations—Mechanical oscillations that cause com-
2.2 ISCC Publications:
ponents of the apparatus to move relative to one another may
Technical Report 2003–1Guide to Material Standards and
cause errors in test results.
Their Use in Color Measurement
6.2.3 Thermal Changes—Temperature changes occurring
3. Terminology
during a test or differences in temperature between testing
locations may affect calibration.
3.1 Terms and definitions in Terminology E284, and Prac-
6.2.4 Power Input Fluctuations—Large changes in the line
tice E1767 and Test Method E2194 are applicable to this test
frequency or supply voltage may cause the apparatus to report
method. See Section 5 of E284 for “Specialized Terminology
erroneous results.
on Gonioapparent Phenomena.”
6.3 Standardization—The system must allow for successful
4. Summary of Test Method
standardization. If the system cannot be standardized, consult
4.1 This test method describes the instrumental geometries,
the manufacturer’s user guide.
including abridged goniospectrometry, used to measure inter-
6.4 Controlling Factors—Accuracy and precision can be
ference pigments. Optical characterization requires color mea-
enhanced by controlling and regulating each factor within the
surementatmultipleilluminationandmultipledetectionangles
constraintsoftheallowableexperimentalerror.Thevaluesand
specified in this procedure. These sets of illumination and
limitsforthesefactorsaretypicallydeterminedexperimentally
detection angles are specified in the test method. Standardiza-
by the user.
tion and verification of the instrument used to measure these
materials are defined. The requirements for selection of speci-
7. Apparatus
mens and measurement procedures are provided. The results
are reported in terms of reflectance factors, CIE tristimulus
7.1 Multiangle Spectrometer—Thistestmethodspecifiesthe
values,andothercolorcoordinatesystemsthatdefinethecolor
required illumination and detection angles of multiangle spec-
of the object. Expected values of precision are presented.
trometers. These multiangle spectrometers are designed spe-
cifically to characterize the optical behavior of materials
5. Significance and Use
coloredwithinterferencepigments.Geometriesarespecifiedin
Section8.Thespectrometermayeitherbeagoniospectrometer
5.1 This test method is designed to provide color data
obtained from spectral reflectance factors at specific illumina- or an abridged goniospectrometer.
tion and detection angles for interference pigments. Informa-
7.1.1 Bi-directional spectrometers or colorimeters with a
tion presented in this test method is based upon data taken on
single angle of measurement; such as 45°:0° or 0°:45°, and
materials exclusively pigmented with interference pigments.
spectrometers using hemispherical geometry cannot ad-
equately characterize the gonioapparency of these materials.
7.1.2 Multiangle spectrometers or colorimeters similar to
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
those specified in Test Method E2194 cannot adequately
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
characterize the gonioapparency of these materials.
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website.
7.2 System Validation Materials—The precision and bias of
Available from the Inter-Society Color Council, 1191 Sunset Hills Road,
Reston, VA 20190, www.iscc.org. the entire measurement system, including calculation of CIE
E2539 − 14 (2021)
TABLE 1 Specified Geometries for Measuring the Color Range
8.2.4 For the reflectance-factor measurement of materials
due to Interference
pigmented with metal-flake pigments and interference
Illumination Detection Aspecular
pigments, additional information is provided by angles speci-
Designation
Angle Angle Angle
fied in Table 2. These angles are used to measure the color
45° -60° -15° 45°:-60° (as-15°)
travel due to pigment flake-orientation effects and light scat-
45° -30° +15° 45°:-30° (as15°)
15° -30° -15° 15°:-30° (as-15°)
tering from the flake edges.
15° 0° +15° 15°:0° (as15°)
9. Test Specimen(s)
Note—This table gives the minimum geometries for the quality control applica-
tion. For other applications, additional geometries; such as 65°:-50° (as15°), may
9.1 Introduction—Measuredvaluesdependonthequalityof
be desirable or needed.
the test specimens. The specimens must be statistically repre-
sentative of the lot being tested and should meet the require-
TABLE 2 Specified Geometries for Measuring the Color due to
Scattering or Orientation ments listed below. If the specimens do not meet these
requirements, include this information in the report (Section
Illumination Detection Aspecular
Designation
Angle Angle Angle
14).
45° -30° 15° 45°:-30° (as15°)*
45° -20° 25° 45°:-20° (as25°) 9.2 Specimen Handling—Handle the specimens carefully.
45° 0° 45° 45°:0° (as45°)*
Touch them by their edges only. Never lay the measurement
45° 30° 75° 45°:30° (as75°)
surface of the specimen down on another surface or stack
45° 65° 110° 45°:65°
(as110°)* specimens without a protective medium between them as
recommended by the provider.
Note—The three angles designated with an asterisk (*), refer to preferred angles
for critical measurements as specified in Test Method E2194.
9.3 Specimen Cleaning—If necessary, clean the specimens
Note—Given a geometric configuration, the reverse geometry is considered
following the providers’ recommended cleaning procedure.
equivalent, if all other components of the instrument design are equivalent.
9.4 Specimen Conditioning—Allow specimens to stabilize
inthemeasurementenvironmentforatimeperiodagreedtoby
tristimulus values, should be determined by periodic measure-
the parties concerned.
ment of known, calibrated, verification standards. These stan-
dards are supplied by instrument manufacturers or obtained
9.5 Specimen Physical Requirements:
separately.
9.5.1 For test specimens that will be assessed visually, the
sizeshallbeatleast8by8cm(approximately3by3in.).This
8. Geometric Conditions
specimen size is well suited for both visual assessment and
8.1 The angles of illumination and detection are critical to
instrumental measurement. See also 12.2.
multiangle measurements of materials pigmented with inter-
NOTE 3—This recommendation for specimen size corresponds to the
ference pigments.
physicalsizerequiredforobservationbytheCIE1964StandardObserver
(10°). The specimen must subtend at least 10° when being observed.
8.2 Recommended Geometries:
Observation usually occurs at approximately 45 cm (17.7 in.) from the
8.2.1 All geometries cited here are uniplanar.
eye.
8.2.2 Geometry Designation—The angles of illumination
9.5.2 The surface of the specimen should be planar.
and detection will be specified as illumination anormal angle,
detection anormal angle, and detection aspecular angle en-
9.6 Specimen Optical Requirements:
closed in parenthesis. See Practice E1767. For the example of
9.6.1 Uniformity—Reference and test specimens should be
an illumination angle of 45° and a detection angle of -30°
uniformincolorandappearance.Formaterialspigmentedwith
(implying an aspecular angle of 15°), the geometry should be
interference or metallic pigments, measurements on different
designated as 45°:-30° (as 15°).
locations on the sample are necessary to assess the degree of
non-uniformity. These data are also useful for determining the
NOTE 1—For either illumination or detection, an anormal angle is
definedastheanglesubtendedatthepointofincidencebyagivenrayand number of measurements necessary to achieve a value that is
the normal to the surface. An anormal angle is understood to be the
statistically representative of the sample. See Practice E1345.
smaller of the two supplementary angles defined by the ray and the
Additionally, the samples-must be similar in appearance to
normal. In a uniplanar geometry, a ray’s anormal angle has a positive sign
makemeaningfulobservations.Thereshouldbenoappearance
if that ray and the incident ray (illuminant ray) are on the same side of the
of mottling or banding in the specimens.
normal.
NOTE 2—The aspecular angle is the detection angle measured away
9.6.2 Gloss—Specimens should be uniform and similar in
from the specular direction, in the illumination plane. Positive values of
gloss when viewed in a lighting booth.
the aspecular angle are in the direction toward the illumination axis.
9.6.3 Surface Texture—The specimens being compared
8.2.3 For the reflectance-factor measurements of interfer-
should have substantially similar surface textures. Orange peel
ence pigments, the instrument’s illumination and detection
is a common example of surface texture.
angles shall conform to the angles as specified in Table 1.
9.6.4 Orientation—Consistent orientation of the specimen
These angles are required to measure the range of colors
forpresentationtothemeasuringinstrumentmustbecontrolled
exhibited by interference pigments.
for repeatable measurements. This is necessary to minimize
errors due to indiscriminate matching of the directionality of
ISCC Technical Report 2003–1. the specimen to that of the instrument.
E2539 − 14 (2021)
10. Instrument Standardization 12.1.1 Select the illumination and detection geometries.
See Section 8 for the specification of angles when measuring
10.1 Standardization is necessary to adjust the instruments
gonioapparentmaterialspigmentedwithinterferencepigments.
output to correspond to a previously established calibration
12.1.2 Select the desired standard observer function.
using one or more homogeneous specimens or reference
12.1.3 Select the desired illuminant.
materials. For the measurement of reflectance factor, full scale
12.1.4 Select the desired CIE colorimetric space such as
and zero standardization are necessary. See Practice E1164.
CIELAB.
10.2 Full-Scale Standardization Plaque—A standardization
12.2 Variation in measurements of gonioapparent materials
plaque with assigned spectral reflectance factors relative to the
is largely due to the inherent non-uniformity of these materials
perfect reflecting diffuser, traceable to a national standardizing
and the difficulty in positioning non flat samples relative to the
laboratory, for each illumination and detection angle is re-
measurement device.
quired to standardize the instrument. The instrument manufac-
turer typically supplies and assigns the standardization values 12.3 Averaging the values made
...