ASTM E2539-08

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Designation: E2539 – 08
Standard Practice 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. A number 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 Practice, E2539, specifies the color
measurement of interference pigments at various illumination and detection angles.
1. Scope for quality control purposes, interference pigments are best
evaluated in a masstone product form. In some cases this
1.1 This practice covers the instrumental requirements and
product form may be the final product form, or more typically
required parameters needed to make instrumental color mea-
a qualified simulation of the intended product form (such as a
surements of thin film interference pigments. This practice is
paint drawdown) that in terms of color and appearance
designed to encompass interference pigments used in architec-
correlates to final product application.
tural applications, automobiles, coatings, cosmetics, inks,
1.7 This standard does not address the requirements for
packaging, paints, plastics, printing, security, and other appli-
characterizing materials containing metal flake pigments. Mea-
cations.
surements of the optical characteristics of materials containing
1.2 Characterization of the optical behavior of materials
metal flake pigments are described in Practice E2194.
colored with interference pigments requires measurement at
1.8 The values stated in SI units are to be regarded as the
multiple angles of illumination and detection.
standard. The values given in parentheses are for information
1.3 Datatakenutilizingthispracticearequantitativeandare
only.
appropriate for quality control of interference pigment color.
1.9 This standard does not purport to address all of the
1.4 The measurement results are usually expressed as re-
safety concerns, if any, associated with its use. It is the
flectance factors, tristimulus color values, or as CIE L*a*b*
responsibility of the user of this standard to establish appro-
color coordinates and color difference.
priate safety and health practices and determine the applica-
1.5 The totality of data taken may not be necessary for
bility of regulatory limitations prior to use.
evaluatingmixturesalsocontainingnon-interferencepigments.
The committee is investigating and evaluating the appropriate-
2. Referenced Documents
ness of this practice for those materials. It is the responsibility
2.1 ASTM Standards:
of the users to determine the applicability of this practice for
E284 Terminology of Appearance
their specific applications.
E308 Practice for Computing the Colors of Objects by
1.6 Interference pigments are typically evaluated for color
Using the CIE System
and color appearance in a medium, such as paint or ink. The
E805 Practice for Identification of Instrumental Methods of
gonioapparent effect depends strongly on the physical and
Color or Color-Difference Measurement of Materials
chemical properties of the medium. Some of the properties
E1164 Practice for Obtaining Spectrometric Data for
affecting color and color appearance include vehicle viscosity,
Object-Color Evaluation
thickness, transparency, and volume solids. As a general rule,
E1345 Practice for Reducing the Effect of Variability of
This practice is under the jurisdiction of ASTM Committee E12 on Color and
Appearance and is the direct responsibility of Subcommittee E12.12 on Gonioap- For referenced ASTM standards, visit the ASTM website, www.astm.org, or
parent Color. contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
Current edition approved Feb. 1, 2008. Published February 2008. DOI: 10.1520/ Standards volume information, refer to the standard’s Document Summary page on
E2539-08. the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
E2539 – 08
Color Measurement by Use of Multiple Measurements 6.2 Factors affecting test results—The following factors are
E1708 Practice for Electronic Interchange of Color and known to affect the test results.
Appearance Data 6.2.1 Extraneous radiation—light from sources other than
E1767 Practice for Specifying the Geometries of Observa- theilluminator(s)andanynear-infrared(NIR)mustbeshielded
tion and Measurement to Characterize the Appearance of from entering the test apparatus.
Materials 6.2.2 Vibrations—mechanical oscillations that cause com-
E2194 PracticeforMultiangleColorMeasurementofMetal ponents of the apparatus to move relative to one another may
Flake Pigmented Materials cause errors in test results.
E2480 Practice for Conducting an Interlaboratory Study to 6.2.3 Thermal changes—temperature changes occurring
Determine the Precision of a Test Method with Multi- during a test or differences in temperature between testing
Valued Measurands locations may affect calibration.
2.2 ISCC Publications: 6.2.4 Power input fluctuations—large changes in the line
Technical Report 2003–1 Guide to Material Standards and frequency or supply voltage may cause the apparatus to report
Their Use in Color Measurement erroneous results.
6.3 Standardization—The system must allow for successful
3. Terminology
standardization. If the system cannot be standardized, consult
the manufacturer’s user guide.
3.1 Terms and definitions in Terminology E284, and Prac-
6.4 Controlling factors—Accuracy and precision can be
tices E1767 and E2194 are applicable to this practice. See
Section 5 of E284 for “Specialized Terminology on Gonioap- enhanced by controlling and regulating each factor within the
constraints of the allowable experimental error.The values and
parent Phenomena.”
limits for these factors are typically determined experimentally
4. Summary of Practice
by the user.
4.1 This practice describes the instrumental geometries,
7. Apparatus
including abridged goniospectrometry, used to measure inter-
7.1 Multi-angle Spectrometer—This practice specifies the
ference pigments. Optical characterization requires color mea-
surementatmultipleilluminationandmultipledetectionangles required illumination and detection angles of multiangle spec-
trometers. These multiangle spectrometers are designed spe-
specified in this procedure. These sets of illumination and
detection angles are specified in the practice. Standardization cifically to characterize the optical behavior of materials
coloredwithinterferencepigments.Geometriesarespecifiedin
and verification of the instrument used to measure these
Section 8.The spectrometer may either be a goniospectrometer
materials are defined. The requirements for selection of speci-
or an abridged goniospectrometer.
mens and measurement procedures are provided. The results
7.1.1 Bi-directional spectrometers or colorimeters with a
are reported in terms of reflectance factors, CIE tristimulus
single angle of measurement; such as 45°:0° or 0°:45°, and
values, and other color coordinate systems that define the color
spectrometers using hemispherical geometry cannot ad-
of the object. Expected values of precision are presented.
equately characterize the gonioapparency of these materials.
5. Significance and Use
7.1.2 Multi-angle spectrometers or colorimeters similar to
those specified in Practice E2194 cannot adequately character-
5.1 This practice is designed to provide color data obtained
ize the gonioapparency of these materials.
from spectral reflectance factors at specific illumination and
7.2 System Validation Materials—The precision and bias of
detection angles for interference pigments. Information pre-
the entire measurement system, including calculation of CIE
sentedinthistestpracticeisbasedupondatatakenonmaterials
tristimulus values, should be determined by periodic measure-
exclusively pigmented with interference pigments.
ment of known, calibrated, verification standards. These stan-
5.2 These data can be used for acceptance testing, design
dards are supplied by instrument manufacturers or obtained
purposes, research, manufacturing control, and quality control.
separately.
5.3 Specimensmustbestatisticallyrepresentativeoftheend
use.
8. Geometric Conditions
5.4 Applicability of this practice for other materials, includ-
8.1 The angles of illumination and detection are critical to
ing combining interference pigments with absorbing and scat-
multiangle measurements of materials pigmented with inter-
tering pigments should be confirmed by the user.
ference pigments.
6. Environmental Conditions
8.2 Recommended Geometries:
8.2.1 All geometries cited here are uniplanar.
6.1 If the standard laboratory conditions listed below
8.2.2 Geometry Designation—The angles of illumination
change during the test or from test to test by an appreciable
and detection will be specified as illumination anormal angle,
amount,theseconditionsmayreduceaccuracyandprecisionof
detection anormal angle, and detection aspecular angle en-
this test method. In some cases these effects may only be
closed in parenthesis. See Practice E1767. For the example of
observed during the performance of the test.
an illumination angle of 45° and a detection angle of -30°
Available from the Inter-Society Color Council, 1191 Sunset Hills Road,
Reston, VA 20190, www.iscc.org. ISCC Technical Report 2003–1.
E2539 – 08
(implying an aspecular angle of 15°), the geometry should be specimens without a protective medium between them as
designated as 45°:-30° (as 15°). recommended by the provider.
9.3 Specimen Cleaning—If necessary, clean the specimens
following the providers’ recommended cleaning procedure.
TABLE 1 Specified Geometries for Measuring the Color Range
9.4 Specimen Conditioning—Allow specimens to stabilize
due to Interference
in the measurement environment for a time period agreed to by
Illumination Detection Aspecular
Designation
the parties concerned.
Angle Angle Angle
9.5 Specimen Physical Requirements :
45° -60° -15° 45°:-60° (as -15°)
9.5.1 For test specimens that will be assessed visually, the
45° -30° +15° 45°:-30° (as 15°)
15° -30° -15° 15°:-30° (as -15°)
size shall be at least 8 by 8 cm (approximately 3 by 3 in.).This
15° 0° +15° 15°:0° (as 15°)
specimen size is well suited for both visual assessment and
Note—This table gives the minimum geometries for the quality control applica- instrumental measurement. See also 12.2.
tion. For other applications, additional geometries; such as 65°:50° (as 15°), may
be desirable or needed. NOTE 3—This recommendation for specimen size corresponds to the
physical size required for observation by the CIE 1964 Standard Observer
(10°). The specimen must subtend at least 10° when being observed.
TABLE 2 Specified Geometries for Measuring the Color due to
Observationusuallyoccursatapproximately45cm(17.7in)fromtheeye.
Scattering or Orientation
Illumination Detection Aspecular
9.5.2 The surface of the specimen should be planar.
Designation
Angle Angle Angle
9.6 Specimen Optical Requirements:
45° -30° 15° 45°:-30° (as 15°)*
9.6.1 Uniformity—Reference and test specimens should be
45° -20° 25° 45°:-20° (as 25°)
uniformincolorandappearance.Formaterialspigmentedwith
45° 0° 45° 45°:0° (as 45°)*
45° 30° 75° 45°:30° (as 75°) interference or metallic pigments, measurements on different
45° 65° 110° 45°:65° (as 110°)*
locations on the sample are necessary to assess the degree of
Note—The three angles designated with an asterisk (*), refer to preferred angles non-uniformity. These data are also useful for determining the
for critical measurements as specified in Practice E2194.
number of measurements necessary to achieve a value that is
Note—Given a geometric configuration, the reverse geometry is considered
statistically representative of the sample. See Practice E1345.
equivalent, if all other components of the instrument design are equivalent.
Additionally, the samples-must be similar in appearance to
make meaningful observations.There should be no appearance
NOTE 1—For either illumination or detection, an anormal angle is
of mottling or banding in the specimens.
defined as the angle subtended at the point of incidence by a given ray and
9.6.2 Gloss—Specimens should be uniform and similar in
the normal to the surface. An anormal angle is understood to be the
gloss when viewed in a lighting booth.
smaller of the two supplementary angles defined by the ray and the
9.6.3 Surface Texture—The specimens being compared
normal. In a uniplanar geometry, a ray’s anormal angle has a positive sign
should have substantially similar surface textures. Orange peel
if that ray and the incident ray (illuminant ray) are on the same side of the
is a common example of surface texture.
normal.
NOTE 2—The aspecular angle is the detection angle measured away
9.6.4 Orientation—Consistent orientation of the specimen
from the specular direction, in the illumination plane. Positive values of
forpresentationtothemeasuringinstrumentmustbecontrolled
the aspecular angle are in the direction toward the illumination axis.
for repeatable measurements. This is necessary to minimize
8.2.3 For the reflectance-factor measurements of interfer- errors due to indiscriminate matching of the directionality of
ence pigments, the instrument’s illumination and detection the specimen to that of the instrument.
angles shall conform to the angles as specified in Table 1.
These angles are required to measure the range of colors 10. Instrument Standardization
exhibited by interference pigments.
10.1 Standardization is necessary to adjust the instruments
8.2.4 For the reflectance-factor measurement of materials
output to correspond to a previously established calibration
pigmented with metal-flake pigments and interference pig-
using one or more homogeneous specimens or reference
ments, additional information is provided by angles specified
materials. For the measurement of reflectance factor, full scale
in Table 2. These angles are used to measure the color travel
and zero standardization are necessary. See Practice E11
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