ASTM_E_2175_-_01_2013.pdf

Designation:E217501(Reapproved 2013)Standard Practice forSpecifying the Geometry of Multiangle Spectrophotometers1This standard is issued under the fixed designation E2175;the number immediately following the designation indicates the year oforiginal adoption or,in the case of revision,the year of last revision.A number in parentheses indicates the year of last reapproval.Asuperscript epsilon()indicates an editorial change since the last revision or reapproval.INTRODUCTIONThe appearance of metallic coatings and plastics usually depends on the directions of illuminationand viewing,a phenomenon called“gonioappearance.”This phenomenon is also observed with othermaterials,such as lustrous textiles and materials containing pearlescent or interference pigments.Thecharacteristic appearance of most such materials is accentuated by directional illumination,such asthat provided by the sun on a clear day or a small lamp at night.The variation in color,as a functionof geometry,is usually measured by spectrophotometry with several specified sets of geometricconditions.Measurement of this kind,at a few selected angles,is called“multianglespectrophotometry,”as distinguished from measurement over a broad range of angles,which is called“goniospectrophotometry.”Spectrophotometric aspects of these measurements,including spectralresolution and linearity of photometric scales,are treated in other standards,including Practice E308and Practice E1164.Practice E1767 provides practice for specifying the geometry of measurements.Retroreflectors exhibit a special kind of gonioappearance,which is treated in otherASTM documents.The present document provides standard practice for specifying influx and efflux angles,angularselectivity,spatial distributions of illuminators and receivers,and angular aspects of standardizing thephotometric scale,that are peculiar to multiangle spectrophotometry.Directional illuminationemphasizes the gonioappearance of most materials,but when interference pigments are used,such asthose used in ink to mark paper currency,the effect is observed with diffuse illumination and varyingangles of viewing,so these materials are also measured with diffuse illumination.1.Scope1.1 This practice provides a way of specifying the angularand spatial conditions of measurement and angular selectivityof a method of measuring the spectral reflectance factors ofopaque gonioapparent materials,for a small number of sets ofgeometric conditions.1.2 Measurements to characterize the appearance of retrore-flective materials are of such a special nature that they aretreated in other ASTM documents and are not included in thescope of this standard.1.3 This standard does not purport to address all 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 AppearanceE308 Practice for Computing the Colors of Objects by Usingthe CIE SystemE1164 Practice for Obtaining Spectrometric Data for Object-Color EvaluationE1767 Practice for Specifying the Geometries of Observa-tion and Measurement to Characterize the Appearance ofMaterials3.Terminology3.1 For definitions of appearance terms used in this practice,refer to Terminology E284.4.Significance and Use4.1 This practice is for the use of manufacturers and users ofinstruments to measure the appearance of gonioapparent1This practice is under the jurisdiction of ASTM Committee E12 on Color andAppearance and is the direct responsibility of Subcommittee E12.03 on Geometry.Current edition approved Oct.1,2013.Published October 2013.Originallyapproved in 2001.Last previous edition approved in 2008 as E2175 01(2008).DOI:10.1520/E2175-01R13.2For 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 standards Document Summary page onthe ASTM website.Copyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959.United States1 materials,those writing standard specifications for suchinstruments,and others who wish to specify precisely thegeometric conditions of multiangle spectrophotometry.Aprominent example of industrial usage is the routine applica-tion of such measurements by material suppliers and automo-bile manufacturers to measure the colors of metallic paints andplastics.5.Components of Apparatus5.1 The apparatus shall consist of one or more illuminatorsand one or more spectrometric receivers at fixed or adjustableangles with respect to a reference plane,a means of positioningspecimens in a reference plane,a means of indicating the areaon the specimen to be measured,shielding to avoid stray light,and a means of displaying spectral or colorimetric data and/orcommunicating such data to a data-recorder or computer.(Thet