1、Designation: E2194 12Standard Practice forMultiangle Color Measurement of Metal Flake PigmentedMaterials1This standard is issued under the fixed designation E2194; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last re
2、vision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.INTRODUCTIONSurfaces that exhibit different colors depending on the angles of illumination or sensing are said tobe “gonioapparent.” Colo
3、rimetric values of reflecting gonioapparent materials are derived fromspectrometric (narrow band) or colorimetric (broad band) measurements of reflectance factor, atvarious aspecular angles. When using spectral values, tristimulus values are computed using the CIEStandard Observer and the spectrum o
4、f the illuminant, as described in Practice E308. This practice,E2194, specifies the measurement of color observed at various aspecular angles.1. Scope1.1 This practice covers the instrumental requirements,standardization procedures, material standards, and parametersneeded to make precise instrument
5、al measurements of thecolors of gonioapparent materials. This practice is designed toencompass gonioapparent materials; such as, automotive coat-ings, paints, plastics, and inks.1.2 This practice addresses measurement of materials con-taining metal flake and pigments. The measurement of mate-rials c
6、ontaining metal flakes requires three angles of measure-ment to characterize the colors of the specimen. The opticalcharacteristics of materials containing pearlescent and interfer-ence materials are not covered by this practice.NOTE 1Data taken by utilizing this practice are for gonio-appearancequa
7、lity control purposes. This procedure may not necessarily supplyappropriate data for spatial-appearance or pigment identification.1.3 The values stated in SI units are to be regarded asstandard. The values given in parentheses are for informationonly.1.4 This standard does not purport to address all
8、 of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2E284 Terminology of A
9、ppearanceE308 Practice for Computing the Colors of Objects byUsing the CIE SystemE805 Practice for Identification of Instrumental Methods ofColor or Color-Difference Measurement of MaterialsE1345 Practice for Reducing the Effect of Variability ofColor Measurement by Use of Multiple MeasurementsE1708
10、 Practice for Electronic Interchange of Color andAppearance DataE2539 Practice for Multiangle Color Measurement of Inter-ference Pigments2.2 CIE Document:3Publication No. 15:2004 Colorimetry2.3 NIST (NBS) Publication:4LC-1017 Standards for Checking the Calibration of Spec-trophotometers2.4 ISO Publi
11、cation:5ISO International Vocabulary of Basic and General Terms inMetrology (VIM)1This practice is under the jurisdiction of ASTM Committee E12 on Color andAppearance and is the direct responsibility of Subcommittee E12.12 on Gonioap-parent Color.Current edition approved April 1, 2012. Published May
12、 2012. Originallyapproved in 2003. Last previous edition approved in 2009 as E2194 - 09. DOI:10.1520/E2194-12.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the st
13、andards Document Summary page onthe ASTM website.3Available from U.S. National Committee of the CIE (International Commissionon Illumination), http:/www.cie.co.at/index_i.e.html.4Available from National Institute of Standards and Technology (NIST), 100Bureau Dr., Stop 1070, Gaithersburg, MD 20899-10
14、70, http:/www.nist.gov.5ISO/IDE/OIML/BIPM, International Vocabulary of Basic and General Terms inMetrology, International Organization for Standardization, Geneva Switzerland,1984.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.3. Te
15、rminology3.1 Terms and definitions in Terminology E284 are appli-cable to this practice. See Section “Specialized Terminology onGonioapparent Phenomena.”3.2 Definitions:3.2.1 Usually the term metallic refers to a metal material.However, this standard employs the alternative definition givenin Termin
16、ology E284 as:3.2.2 metallic, adjpertaining to the appearance of a gonio-apparent material containing metal flakes.3.3 Definitions of metrology terms in ISO InternationalVocabulary of Basic and General Terms in Metrology (VIM)are applicable to this practice.4. Summary of Practice4.1 This practice de
17、scribes the procedures for the spectro-metric and colorimetric measurement of metal flake pigmentedmaterials. The results are reported in terms of CIE tristimulusvalues and other color coordinate systems. Standardization ofthe instrument used to measure these materials is defined.Guidelines are give
18、n for the selection of specimens and ameasurement protocol given. Characterization of these mate-rials requires measurement at a near-specular angle, a mid-specular angle and a far-specular angle. These preferredaspecular angles are 15, 45, and 110.5. Significance and Use5.1 Instrumental Measurement
19、 AnglesThis practice is de-signed to provide color data at specific measurement anglesthat can be utilized for quality control, color matching, andformulating in the characterization of metal flake pigmentedmaterials.5.2 MaterialsThis practice provides meaningful colorinformation for metal flake pig
20、mented materials. This practicehas been tested and verified on paint and coatings, and thesame principles should apply to plastics containing metallicflake. For materials containing pearlescent materials refer toPractice E2539.5.3 UtilizationThis practice is appropriate for measure-ment and characte
21、rization of metal flake pigmented materials.These data may be used for quality control, incoming inspec-tion, or color correction purposes.5.4 Specimen RequirementsEven though a pair of speci-mens have the same color values at three angles, if there aredifferences in gloss, orange peel, texture, or
22、flake orientation,they may not be a visual match.NOTE 2Information presented in this practice is based upon datataken on metallic materials coatings. Applicability of this practice to othermaterials should be confirmed by the user.6. Apparatus6.1 InstrumentThis practice requires measurement atmultip
23、le aspecular angles, usually accomplished by the use ofa multiangle spectrometer as specified in this practice tocharacterize metal flake pigmented materials. Measurementwith a single geometry cannot characterize the gonioappear-ance of these materials.6.2 StandardizationA standardization plaque wit
24、h as-signed spectral reflectance factor or tristimulus values traceableto a national standardizing laboratory for each specified as-pecular angle is required to standardize the instrument. Theinstrument manufacturer typically assigns the values to thisplaque.7. Geometric Conditions7.1 Conventional C
25、olor MeasurementIn general purposecolorimetry, the common geometry involves illuminating at45 and sensing at 0. This geometry is designated 45:0 (45/0).Reverse geometry has the illumination at 0 and the sensing at45. That is, the illuminator and sensing geometries areinterchanged. This reciprocal ge
26、ometry is designated 0:45(0/45). Either geometry is used.7.1.1 A single bi-directional geometry is specified by illu-mination and sensing angles with respect to the normal of theplane of the specimen. Angles are measured relative to thenormal. Angles on the same side of the normal as theillumination
27、 beam are written as positive angles; those on theother side are shown as negative, as shown in Fig. 1.7.2 Multiangle Uniplanar MeasurementThe color of me-tallic materials specimens varies with the angle of view. Thusmeasurements must be taken at more than one aspecular angleto characterize the chan
28、ge of color with angle. The measure-ment geometry for multiangle measurements is specified byaspecular angles. The aspecular angle is the viewing anglemeasured from the specular direction, in the illuminator planeunless otherwise specified. The angle is considered positivewhen measured from the spec
29、ular direction towards the illu-minator axis. Thus, if the specimen is illuminated at 45 to thenormal the specular reflection will be at -45 (See Fig. 1).Sensing at 65 from the normal, and on the same side of normalas the illumination, is sensing 110 away from the speculardirection; that is an aspec
30、ular angle of 110. Thus, theaspecular angle is the sum of the anormal illumination andsensing angles. It has been established that for metallicmaterials or colors, a specific aspecular angle gives the samemeasurement regardless of angle of illumination.7.3 Annular and Circumferential GeometryAnnular
31、 illu-mination provides incident light to a specimen at all azimuthalangles. This type of illumination minimizes the contributionNOTE 1Anormal illumination angle = 45 and anormal sensingangle = 65; therefore, aspecular angle = 45 + 65 = 110.FIG. 1 Example of Illuminating and Sensing GeometryE2194 12
32、2from directional effects such as the venetian blind effect andsurface irregularities. Circumferential illumination is an ap-proximation to annular illumination, incident light being pro-vided from a discrete number of representative azimuthalangles. A large number or an odd number of illuminationso
33、urces more closely approximates annular illumination. An-nular or circumferential illumination minimizes directionaleffects. Therefore, measurements with annular or circumferen-tial illumination may or may not correlate with how thatspecimen appears under directional illumination. For example,this s
34、ystem averaging may cause the measured color values oftwo specimens to be the same or similar, even though thesesame two specimens would not match visually due to the factthat one specimen exhibits the venetian blind effect.7.4 Recommended GeometryThe instrument shall con-form to the following geome
35、tric requirements for measurementof reflectance factor unless otherwise agreed upon between thebuyer and the seller. The preferred aspecular angles formeasurement are 15, 45, and 110.NOTE 3Given a geometric configuration, the reverse geometry isconsidered equivalent, if all other components of the i
36、nstrument design areequivalent; for example, in the example shown in Fig. 1, the same resultwould be obtained with the illumination angle at 65 and the sensing angleat 45. The aspecular angle would still be 110.NOTE 4Measurement angles below are stated in terms of aspecularangles. It has been establ
37、ished that for metallic materials colors, a specificaspecular angle gives the same measurement regardless of angle ofillumination. For pearlescent materials, it is known that color is also afunction of angle of illumination. The importance of this phenomenon inmeasurement of pearlescent and interfer
38、ence materials for color differencefor quality control or color correction purposes has not been established.NOTE 5Uniplanar instruments can measure the venetian blind effect.Circumferential and annular illumination will not quantify this gonioap-parent effect.NOTE 6There are instruments commerciall
39、y available with uniplanar,multiangle geometries that give results that characterize gonioapparentmaterials. These instruments will detect the venetian blind effect and otheranomalies. Table 1 delineates the preferred angles. Note that circumfer-ential geometry is limited to 10 when being observed.T
40、his observation usually occurs at approximately 45 cm (17.7 in.) fromthe eye. This specimen size is well suited for instrumental measurementand visual assessment.8.5.2 The surface of the specimen to be measured should beessentially planar.8.6 Specimen Optical Requirements:8.6.1 UniformityReference s
41、pecimens and test specimensshould be uniform in color and appearance when viewed in alighting booth. They must be similar in appearance to makemeaningful observations. There should be no appearance ofmottling or banding in the specimens.8.6.2 GlossSpecimens should be uniform and similar ingloss when
42、 viewed in a lighting booth.8.6.3 Surface TextureThe standard and batch being com-pared should have substantially similar surface textures. Or-ange peel is a common example of surface texture.8.6.4 Specimen Flake DistributionExamine the speci-mens to ensure that they have similar flake size and dist
43、ribu-tion. Dissimilar flake distributions will cause results to varysignificantly.8.6.5 OrientationConsistent orientation of the specimenfor presentation to the measuring instrument must be controlledfor repeatable measurements. This is necessary to minimizeerrors due to indiscriminate matching of t
44、he directionality ofthe specimen to that of the instrument.9. Instrument Standardization9.1 Standardization is essential to ensure that spectrometricor tristimulus measurements with minimum bias are reported.For the measurement of reflectance factor, two standardizationsare required, namely,9.1.1 Op
45、tical Zero (0) Level StandardizationTo verify theoptical zero, the instrument manufacturer normally supplies ahighly polished black glass or a black trap that has an assignedreflectance factor value.9.1.2 Full Scale StandardizationTo standardize the instru-ment relative to the perfect reflecting dif
46、fuser, the instrumentmanufacturer should provide a standardization plaque withmultiangle calibration traceable to a standardizing laboratory.9.1.3 Photometric Scale ValidationTo ascertain properstandardization, measure a reference plaque immediately afterthe standardization sequence and validate tha
47、t the measuredvalues agree with the assigned values within 0.05 reflectanceunit.9.1.4 DiscussionTypically a neutral gray of 50 % reflec-tance is used for this purpose.10. Instrumental Performance Verification10.1 The use of validation standards to verify spectrometricperformance of an instrument is
48、recommended. These stan-dards are readily available from multiple sources. The instru-ment user must assume responsibility for obtaining thesestandards and their appropriate use. See NIST LC-1017 forfurther discussion.10.2 It is recommended that a user measure a durablegonioapparent specimen over ti
49、me, recording and comparingvalues to ascertain proper instrument performance.11. Measurement Procedure11.1 Select Measurement VariablesSelect and validate theinstrumental configuration before measurement.11.1.1 Select the desired illuminating and sensing geom-etries. See Section 6 for definition of angles when measuringgonioapparent materials.11.1.2 Select the desired observer.11.1.3 Select the desired illuminant.11.1.4 Select the desired colorimetric space, for example,CIELAB.11.2 Variation in measurements of gonioapparent materials
