ASTM E2194-14(2017)

Standard Test Method for Multiangle Color Measurement of Metal Flake Pigmented Materials

SIGNIFICANCE AND USE
5.1 Instrumental Measurement Angles—This test method is designed to provide color data at specific measurement angles that can be utilized for quality control, color matching, and formulating in the characterization of metal flake pigmented materials.  
5.2 Materials—This test method provides meaningful color information for metal flake pigmented materials. This test method has been tested and verified on paint and coatings, and the same principles should apply to plastics containing metallic flake. For materials containing pearlescent materials refer to Test Method E2539.  
5.3 Utilization—This test method is appropriate for measurement and characterization of metal flake pigmented materials. These data may be used for quality control, incoming inspection, or color correction purposes.  
5.4 Specimen Requirements—Even though a pair of specimens have the same color values at three angles, if there are differences in gloss, orange peel, texture, or flake orientation, they may not be a visual match.
Note 2: Information presented in this test method is based upon data taken on metallic materials coatings. Applicability of this test method to other materials should be confirmed by the user.
SCOPE
1.1 This test method covers the instrumental requirements, standardization procedures, material standards, and parameters needed to make precise instrumental measurements of the colors of gonioapparent materials. This test method is designed to encompass gonioapparent materials; such as, automotive coatings, paints, plastics, and inks.  
1.2 This test method addresses measurement of materials containing metal flake and pigments. The measurement of materials containing metal flakes requires three angles of measurement to characterize the colors of the specimen. The optical characteristics of materials containing pearlescent and interference materials are not covered by this test method.
Note 1: Data taken by utilizing this test method are for gonio-appearance quality control purposes. This procedure may not necessarily supply appropriate data for spatial-appearance or pigment identification.  
1.3 The values stated in SI units are to be regarded as standard. The values given in parentheses are for information only.  
1.4 This standard does not purport to address all of the safety concerns, 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.  
1.5 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.

General Information

• Status: Historical
• Publication Date: 31-May-2017
• ICS: 17.180.20 - Colours and measurement of light
• Technical Committee: E12 - Color and Appearance
• Drafting Committee: E12.12 - Gonioapparent Color

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: E2194 − 14 (Reapproved 2017)
Standard Test Method for
Multiangle Color Measurement of Metal Flake Pigmented
Materials
This standard is issued under the fixed designation E2194; 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
Surfaces that exhibit different colors depending on the angles of illumination or sensing are said to
be “gonioapparent.” Colorimetric values of reflecting gonioapparent materials are derived from
spectrometric (narrow band) or colorimetric (broad band) measurements of reflectance factor, at
various aspecular angles. When using spectral values, tristimulus values are computed using the CIE
StandardObserverandthespectrumoftheilluminant,asdescribedinPracticeE308.Thistestmethod,
E2194, specifies the measurement of color observed at various aspecular angles.
1. Scope ization established in the Decision on Principles for the
Development of International Standards, Guides and Recom-
1.1 This test method covers the instrumental requirements,
mendations issued by the World Trade Organization Technical
standardization procedures, material standards, and parameters
Barriers to Trade (TBT) Committee.
needed to make precise instrumental measurements of the
colorsofgonioapparentmaterials.Thistestmethodisdesigned
2. Referenced Documents
to encompass gonioapparent materials; such as, automotive
coatings, paints, plastics, and inks.
2.1 ASTM Standards:
1.2 This test method addresses measurement of materials
E284Terminology of Appearance
containing metal flake and pigments. The measurement of
E308PracticeforComputingtheColorsofObjectsbyUsing
materials containing metal flakes requires three angles of
the CIE System
measurement to characterize the colors of the specimen. The
E805Practice for Identification of Instrumental Methods of
optical characteristics of materials containing pearlescent and
Color or Color-Difference Measurement of Materials
interference materials are not covered by this test method.
E1345Practice for Reducing the Effect of Variability of
NOTE 1—Data taken by utilizing this test method are for gonio-
Color Measurement by Use of Multiple Measurements
appearance quality control purposes. This procedure may not necessarily
E1708Practice for Electronic Interchange of Color and
supply appropriate data for spatial-appearance or pigment identification.
Appearance Data
1.3 The values stated in SI units are to be regarded as
E2539Test Method for Multiangle Color Measurement of
standard. The values given in parentheses are for information
Interference Pigments
only.
2.2 CIE Document:
1.4 This standard does not purport to address all of the
Publication No. 15Colorimetry
safety concerns, if any, associated with its use. It is the
responsibility of the user of this standard to establish appro- 4
2.3 NIST (NBS) Publication:
priate safety and health practices and determine the applica-
LC-1017StandardsforCheckingtheCalibrationofSpectro-
bility of regulatory limitations prior to use.
photometers
1.5 This international standard was developed in accor-
dance with internationally recognized principles on standard-
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
This test method is under the jurisdiction of ASTM Committee E12 on Color Standards volume information, refer to the standard’s Document Summary page on
and Appearance and is the direct responsibility of Subcommittee E12.12 on the ASTM website.
Gonioapparent Color. Available from CIE (International Commission on Illumination) at
CurrenteditionapprovedJune1,2017.PublishedJuly2017.Originallyapproved www.cie.co.at or www.techstreet.com.
in 2003. Last previous edition approved in 2014 as E2194– 14. DOI: 10.1520/ Available from National Institute of Standards and Technology (NIST), 100
E2194-14R17. Bureau Dr., Stop 1070, Gaithersburg, MD 20899-1070, http://www.nist.gov.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
E2194 − 14 (2017)
2.4 ISO Publication: 6. Apparatus
ISO InternationalVocabulary of Basic and GeneralTerms in
6.1 Instrument—This test method requires measurement at
Metrology (VIM)
multiple aspecular angles, usually accomplished by the use of
a multiangle spectrometer as specified in this test method to
3. Terminology
characterize metal flake pigmented materials. Measurement
3.1 Terms and definitions in Terminology E284 are appli-
with a single geometry cannot characterize the gonioappear-
cable to this test method. See Section “Specialized Terminol-
ance of these materials.
ogy on Gonioapparent Phenomena.”
6.2 Standardization—A standardization plaque with as-
3.2 Definitions:
signedspectralreflectancefactorortristimulusvaluestraceable
3.2.1 Usually the term metallic refers to a metal material.
to a national standardizing laboratory for each specified as-
However,thisstandardemploysthealternativedefinitiongiven
pecular angle is required to standardize the instrument. The
in Terminology E284 as:
instrument manufacturer typically assigns the values to this
3.2.2 metallic, adj—pertainingtotheappearanceofagonio-
plaque.
apparent material containing metal flakes.
7. Geometric Conditions
3.3 Definitions of metrology terms in ISO International
7.1 Conventional Color Measurement—In general purpose
Vocabulary of Basic and General Terms in Metrology (VIM)
colorimetry, the common geometry involves illuminating at
are applicable to this test method.
45°andsensingat0°.Thisgeometryisdesignated45:0(45/0).
4. Summary of Test Method
Reverse geometry has the illumination at 0° and the sensing at
45°. That is, the illuminator and sensing geometries are
4.1 This test method describes the procedures for the
interchanged. This reciprocal geometry is designated 0:45
spectrometric and colorimetric measurement of metal flake
(0/45). Either geometry is used.
pigmented materials. The results are reported in terms of CIE
7.1.1 A single bi-directional geometry is specified by illu-
tristimulus values and other color coordinate systems. Stan-
mination and sensing angles with respect to the normal of the
dardizationoftheinstrumentusedtomeasurethesematerialsis
plane of the specimen. Angles are measured relative to the
defined. Guidelines are given for the selection of specimens
normal. Angles on the same side of the normal as the
and a measurement protocol given. Characterization of these
illumination beam are written as positive angles; those on the
materials requires measurement at a near-specular angle, a
other side are shown as negative, as shown in Fig. 1.
mid-specular angle and a far-specular angle. These preferred
aspecular angles are 15°, 45°, and 110°.
7.2 Multiangle Uniplanar Measurement—The color of me-
tallic materials specimens varies with the angle of view. Thus
5. Significance and Use
measurements must be taken at more than one aspecular angle
5.1 Instrumental Measurement Angles—This test method is
to characterize the change of color with angle. The measure-
designed to provide color data at specific measurement angles ment geometry for multiangle measurements is specified by
that can be utilized for quality control, color matching, and aspecular angles. The aspecular angle is the viewing angle
formulating in the characterization of metal flake pigmented measured from the specular direction, in the illuminator plane
materials. unless otherwise specified. The angle is considered positive
when measured from the specular direction towards the illu-
5.2 Materials—This test method provides meaningful color
minator axis.Thus, if the specimen is illuminated at 45° to the
information for metal flake pigmented materials. This test
normal the specular reflection will be at -45° (See Fig. 1).
method has been tested and verified on paint and coatings, and
Sensingat65°fromthenormal,andonthesamesideofnormal
thesameprinciplesshouldapplytoplasticscontainingmetallic
as the illumination, is sensing 110° away from the specular
flake. For materials containing pearlescent materials refer to
Test Method E2539.
5.3 Utilization—This test method is appropriate for mea-
surement and characterization of metal flake pigmented mate-
rials. These data may be used for quality control, incoming
inspection, or color correction purposes.
5.4 Specimen Requirements—Even though a pair of speci-
mens have the same color values at three angles, if there are
differences in gloss, orange peel, texture, or flake orientation,
they may not be a visual match.
NOTE 2—Information presented in this test method is based upon data
taken on metallic materials coatings. Applicability of this test method to
other materials should be confirmed by the user.
NOTE 1—Anormal illumination angle=45° and anormal sensing
ISO/IDE/OIML/BIPM,InternationalVocabularyofBasicandGeneralTermsin
angle=65°; therefore, aspecular angle=45+65=110°.
Metrology, International Organization for Standardization, Geneva Switzerland,
1984. FIG. 1 Example of Illuminating and Sensing Geometry
E2194 − 14 (2017)
direction; that is an aspecular angle of 110°. Thus, the
aspecular angle is the sum of the anormal illumination and
sensing angles. It has been established that for metallic
materials or colors, a specific aspecular angle gives the same
measurement regardless of angle of illumination.
7.3 Annular and Circumferential Geometry—Annular illu-
mination provides incident light to a specimen at all azimuthal
angles. This type of illumination minimizes the contribution
from directional effects such as the venetian blind effect and
surface irregularities. Circumferential illumination is an ap-
proximation to annular illumination, incident light being pro-
NOTE 1—Solid lines indicate preferred angles.
vided from a discrete number of representative azimuthal
FIG. 2 Diagram of Aspecular Angles
angles. A large number or an odd number of illumination
sources more closely approximates annular illumination. An-
nular or circumferential illumination minimizes directional
effects. Therefore, measurements with annular or circumferen-
to be reflected in a direction slightly away from the nominal
tial illumination may or may not correlate with how that specular direction. Measurement at 15° from the specular
specimen appears under directional illumination. For example,
minimizes the effects of surface imperfections encountered in
this system averaging may cause the measured color values of most practical industrial specimens. Differences in surface
two specimens to be the same or similar, even though these
texture may result from spray application differences which
same two specimens would not match visually due to the fact can cause flake orientation differences. Measurement at 20° or
that one specimen exhibits the venetian blind effect.
25° from specular may be chosen when less sensitivity to
application differences between standard and batch is desired.
7.4 Recommended Geometry—The instrument shall con-
In critical color matching applications, batches should be
formtothefollowinggeometricrequirementsformeasurement
resampled and resprayed to eliminate surface differences and
of reflectance factor unless otherwise agreed upon between the
measurements shall be performed at 15°.
buyer and the seller. The preferred aspecular angles for
7.4.2 Mid-specular Angle—The mid-specular color mea-
measurement are 15°, 45°, and 110°.
surement shall be at an aspecular angle of 45° conforming to
NOTE 3—Given a geometric configuration, the reverse geometry is
the geometrical specifications of CIE 15:2004.
consideredequivalent,ifallothercomponentsoftheinstrumentdesignare
7.4.3 Far-specular Angle—Visual observation of color dif-
equivalent; for example, in the example shown in Fig. 1, the same result
ferences in a few cases detects sidetone scattering better at
wouldbeobtainedwiththeilluminationangleat65°andthesensingangle
at 45°. The aspecular angle would still be 110°. anglesfurtherawayfromspecular;hence,110°isthepreferred
NOTE 4—Measurement angles below are stated in terms of aspecular
aspecular angle for far-specular measurement. In most but not
angles.Ithasbeenestablishedthatformetallicmaterialscolors,aspecific
all cases, angles down to 70° give acceptable results.
aspecular angle gives the same measurement regardless of angle of
(Warning—Visual assessments of gonioapparent matches
illumination. For pearlescent materials, it is known that color is also a
typically cover a wide range of aspecular angles, from very
function of angle of illumination. The importance of this phenomenon in
measurementofpearlescentandinterferencematerialsforcolordifference nearspecular,allthewaytofar-specularanglesof110°oreven
for quality control or color correction purposes has not been established.
higher. Therefore, instrumental measurement at far-specular
NOTE 5—Uniplanar instruments can measure the venetian blind effect.
angles below 110° may occasionally result in measurements
Circumferential and annular illumination will not quantify this gonioap-
not agreeing with typical visual assessments. This will occur
parent effect.
when specimens are an acceptable visual and instrumental
NOTE 6—There are instruments commercially available with uniplanar,
multiangle geometries that give results that characterize gonioapparent match at angles such as 75° but unacceptable at 110°.)
materials.Theseinstrumentswilldetectthevenetianblindeffectandother
7.4.4 Illuminating and Sensing Beam Aperture Angles—The
anomalies. Table 1 delineates the preferred angles. Note that circumfer-
illuminating beam aperture angle and the sensing beam aper-
ential geometry is limited to <90° aspecular angle. With the variety of
ture angle must be less than 8°.
instrumentation in common usage, it is incumbent upon the user to
determine if an instrument with angles other than the preferred angles is
appropriate in their application. Fig. 2 8. Test Specimen
7.4.1 Near Specular Angle—The near specular angle used
8.1 Measured values depend on the quality of the test
shouldbeasclosetothespeculardirectionaspossible,without
specimens. The specimens must be statistically representative
detecting specular light. Surface imperfections can cause light
of the lot being tested and should meet the requirements listed
below. If the specimens do not meet these requirements,
include this information in Section 13.
TABLE 1 Preferred Angles
8.2 Specimen Handling—Handle the specimens carefully.
Uniplanar Angle Preferred Angle
Touch them by their edg
...

This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Because
it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
Designation: E2194 − 14 E2194 − 14 (Reapproved 2017)
Standard Test Method for
Multiangle Color Measurement of Metal Flake Pigmented
Materials
This standard is issued under the fixed designation E2194; 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
Surfaces that exhibit different colors depending on the angles of illumination or sensing are said to
be “gonioapparent.” Colorimetric values of reflecting gonioapparent materials are derived from
spectrometric (narrow band) or colorimetric (broad band) measurements of reflectance factor, at
various aspecular angles. When using spectral values, tristimulus values are computed using the CIE
Standard Observer and the spectrum of the illuminant, as described in Practice E308. This test method,
E2194, specifies the measurement of color observed at various aspecular angles.
1. Scope
1.1 This test method covers the instrumental requirements, standardization procedures, material standards, and parameters
needed to make precise instrumental measurements of the colors of gonioapparent materials. This test method is designed to
encompass gonioapparent materials; such as, automotive coatings, paints, plastics, and inks.
1.2 This test method addresses measurement of materials containing metal flake and pigments. The measurement of materials
containing metal flakes requires three angles of measurement to characterize the colors of the specimen. The optical characteristics
of materials containing pearlescent and interference materials are not covered by this test method.
NOTE 1—Data taken by utilizing this test method are for gonio-appearance quality control purposes. This procedure may not necessarily supply
appropriate data for spatial-appearance or pigment identification.
1.3 The values stated in SI units are to be regarded as standard. The values given in parentheses are for information only.
1.4 This standard does not purport to address all of the safety concerns, 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.
1.5 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.
2. Referenced Documents
2.1 ASTM Standards:
E284 Terminology of Appearance
E308 Practice for Computing the Colors of Objects by Using the CIE System
E805 Practice for Identification of Instrumental Methods of Color or Color-Difference Measurement of Materials
E1345 Practice for Reducing the Effect of Variability of Color Measurement by Use of Multiple Measurements
E1708 Practice for Electronic Interchange of Color and Appearance Data
E2539 Test Method for Multiangle Color Measurement of Interference Pigments
2.2 CIE Document:
Publication No. 15:200415 Colorimetry
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 Gonioapparent
Color.
Current edition approved Nov. 1, 2014June 1, 2017. Published November 2014July 2017. Originally approved in 2003. Last previous edition approved in 20122014 as
E2194 – 12.14. DOI: 10.1520/E2194-14.10.1520/E2194-14R17.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
Available from U.S. National Committee of the CIE (International Commission on Illumination), http://www.cie-usnc.orgIllumination) at
www.cie.co.at or http://www.techstreet.com/cie.www.techstreet.com.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
E2194 − 14 (2017)
2.3 NIST (NBS) Publication:
LC-1017 Standards for Checking the Calibration of Spectrophotometers
2.4 ISO Publication:
ISO International Vocabulary of Basic and General Terms in Metrology (VIM)
3. Terminology
3.1 Terms and definitions in Terminology E284 are applicable to this test method. See Section “Specialized Terminology on
Gonioapparent Phenomena.”
3.2 Definitions:
3.2.1 Usually the term metallic refers to a metal material. However, this standard employs the alternative definition given in
Terminology E284 as:
3.2.2 metallic, adj—pertaining to the appearance of a gonioapparent material containing metal flakes.
3.3 Definitions of metrology terms in ISO International Vocabulary of Basic and General Terms in Metrology (VIM) are
applicable to this test method.
4. Summary of Test Method
4.1 This test method describes the procedures for the spectrometric and colorimetric measurement of metal flake pigmented
materials. The results are reported in terms of CIE tristimulus values and other color coordinate systems. Standardization of the
instrument used to measure these materials is defined. Guidelines are given for the selection of specimens and a measurement
protocol given. Characterization of these materials requires measurement at a near-specular angle, a mid-specular angle and a
far-specular angle. These preferred aspecular angles are 15°, 45°, and 110°.
5. Significance and Use
5.1 Instrumental Measurement Angles—This test method is designed to provide color data at specific measurement angles that
can be utilized for quality control, color matching, and formulating in the characterization of metal flake pigmented materials.
5.2 Materials—This test method provides meaningful color information for metal flake pigmented materials. This test method
has been tested and verified on paint and coatings, and the same principles should apply to plastics containing metallic flake. For
materials containing pearlescent materials refer to Test Method E2539.
5.3 Utilization—This test method is appropriate for measurement and characterization of metal flake pigmented materials. These
data may be used for quality control, incoming inspection, or color correction purposes.
5.4 Specimen Requirements—Even though a pair of specimens have the same color values at three angles, if there are differences
in gloss, orange peel, texture, or flake orientation, they may not be a visual match.
NOTE 2—Information presented in this test method is based upon data taken on metallic materials coatings. Applicability of this test method to other
materials should be confirmed by the user.
6. Apparatus
6.1 Instrument—This test method requires measurement at multiple aspecular angles, usually accomplished by the use of a
multiangle spectrometer as specified in this test method to characterize metal flake pigmented materials. Measurement with a single
geometry cannot characterize the gonioappearance of these materials.
6.2 Standardization—A standardization plaque with assigned spectral reflectance factor or tristimulus values traceable to a
national standardizing laboratory for each specified aspecular angle is required to standardize the instrument. The instrument
manufacturer typically assigns the values to this plaque.
7. Geometric Conditions
7.1 Conventional Color Measurement—In general purpose colorimetry, the common geometry involves illuminating at 45° and
sensing at 0°. This geometry is designated 45:0 (45/0). Reverse geometry has the illumination at 0° and the sensing at 45°. That
is, the illuminator and sensing geometries are interchanged. This reciprocal geometry is designated 0:45 (0/45). Either geometry
is used.
7.1.1 A single bi-directional geometry is specified by illumination and sensing angles with respect to the normal of the plane
of the specimen. Angles are measured relative to the normal. Angles on the same side of the normal as the illumination beam are
written as positive angles; those on the other side are shown as negative, as shown in Fig. 1.
Available from National Institute of Standards and Technology (NIST), 100 Bureau Dr., Stop 1070, Gaithersburg, MD 20899-1070, http://www.nist.gov.
ISO/IDE/OIML/BIPM, International Vocabulary of Basic and General Terms in Metrology, International Organization for Standardization, Geneva Switzerland, 1984.
E2194 − 14 (2017)
NOTE 1—Anormal illumination angle = 45° and anormal sensing angle = 65°; therefore, aspecular angle = 45 + 65 = 110°.
FIG. 1 Example of Illuminating and Sensing Geometry
7.2 Multiangle Uniplanar Measurement—The color of metallic materials specimens varies with the angle of view. Thus
measurements must be taken at more than one aspecular angle to characterize the change of color with angle. The measurement
geometry for multiangle measurements is specified by aspecular angles. The aspecular angle is the viewing angle measured from
the specular direction, in the illuminator plane unless otherwise specified. The angle is considered positive when measured from
the specular direction towards the illuminator axis. Thus, if the specimen is illuminated at 45° to the normal the specular reflection
will be at -45° (See Fig. 1). Sensing at 65° from the normal, and on the same side of normal as the illumination, is sensing 110°
away from the specular direction; that is an aspecular angle of 110°. Thus, the aspecular angle is the sum of the anormal
illumination and sensing angles. It has been established that for metallic materials or colors, a specific aspecular angle gives the
same measurement regardless of angle of illumination.
7.3 Annular and Circumferential Geometry—Annular illumination provides incident light to a specimen at all azimuthal angles.
This type of illumination minimizes the contribution from directional effects such as the venetian blind effect and surface
irregularities. Circumferential illumination is an approximation to annular illumination, incident light being provided from a
discrete number of representative azimuthal angles. A large number or an odd number of illumination sources more closely
approximates annular illumination. Annular or circumferential illumination minimizes directional effects. Therefore, measurements
with annular or circumferential illumination may or may not correlate with how that specimen appears under directional
illumination. For example, this system averaging may cause the measured color values of two specimens to be the same or similar,
even though these same two specimens would not match visually due to the fact that one specimen exhibits the venetian blind
effect.
7.4 Recommended Geometry—The instrument shall conform to the following geometric requirements for measurement of
reflectance factor unless otherwise agreed upon between the buyer and the seller. The preferred aspecular angles for measurement
are 15°, 45°, and 110°.
NOTE 3—Given a geometric configuration, the reverse geometry is considered equivalent, if all other components of the instrument design are
equivalent; for example, in the example shown in Fig. 1, the same result would be obtained with the illumination angle at 65° and the sensing angle at
45°. The aspecular angle would still be 110°.
NOTE 4—Measurement angles below are stated in terms of aspecular angles. It has been established that for metallic materials colors, a specific
aspecular angle gives the same measurement regardless of angle of illumination. For pearlescent materials, it is known that color is also a function of
angle of illumination. The importance of this phenomenon in measurement of pearlescent and interference materials for color difference for quality control
or color correction purposes has not been established.
NOTE 5—Uniplanar instruments can measure the venetian blind effect. Circumferential and annular illumination will not quantify this gonioapparent
effect.
NOTE 6—There are instruments commercially available with uniplanar, multiangle geometries that give results that characterize gonioapparent
materials. These instruments will detect the venetian blind effect and other anomalies. Table 1 delineates the preferred angles. Note that circumferential
geometry is limited to <90° aspecular angle. With the variety of instrumentation in common usage, it is incumbent upon the user to determine if an
instrument with angles other than the preferred angles is appropriate in their application. Fig. 2
TABLE 1 Preferred Angles
Uniplanar Angle Preferred Angle
Near specular 15°
Mid-specular angle 45°
Far-specular angle 110°
NOTE 1—Other geometries in common usage are: 25°, 70°, or 75°.
E2194 − 14 (2017)
NOTE 1—Solid lines indicate preferred angles.
FIG. 2 Diagram of Aspecular Angles
7.4.1 Near Specular Angle—The near specular angle used should be as close to the specular direction as possible, without
detecting specular light. Surface imperfections can cause light to be reflected in a direction slightly away from the nominal specular
direction. Measurement at 15° from the specular minimizes the effects of surface imperfections encountered in most practical
industrial specimens. Differences in surface texture may result from spray application differences which can cause flake orientation
differences. Measurement at 20° or 25° from specular may be chosen when less sensitivity to application differences between
standard and batch is desired. In critical color matching applications, batches should be resampled and resprayed to eliminate
surface differences and measurements shall be performed at 15°.
7.4.2 Mid-specular Angle—The mid-specular color measurement shall be at an aspecular angle of 45° conforming to the
geometrical specifications of CIE 15:2004.
7.4.3 Far-specular Angle—Visual observation of color differences in a few cases detects sidetone scattering better at angles
further away from specular; hence, 110° is the preferred aspecular angle for far-specular measurement. In most but not all cases,
angles down to 70° give acceptable results. (Warning—Visual assessments of gonioapparent matches typically cover a wide range
of aspecular angles, from very near specular, all the way to far-specular angles of 110° or
...