1、Designation: E 259 06Standard Practice forPreparation of Pressed Powder White Reflectance FactorTransfer Standards for Hemispherical and Bi-DirectionalGeometries1This standard is issued under the fixed designation E 259; the number immediately following the designation indicates the year oforiginal
2、adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) indicates an editorial change since the last revision or reapproval.INTRODUCTIONThe internationally accepted standard of reflectance is the perfect
3、 reflecting diffuser. This idealreflecting surface reflects 100 % of the incident radiant power such that the radiance is the same forall directions within the hemisphere above the surface. No physical realization of this standard exists.Optical properties of standards prepared from pressed plaques
4、of magnesium carbonate (MgCO3),barium sulfate (BaSO4), or polytetrafluoroethylene (PTFE) can approximate an ideal standard. Forfurther information see CIE Publication No. 46 (1).2The principal use of a white reflectance factorstandard is to transfer an absolute scale of reflectance to a more durable
5、 material or from oneinstrument to another. In theory, it should be easy to do this transfer from first principles. In practice,one is likely to need values for parameters that are unknown, proprietary, or require a high level ofskill. Some, but not all, of those parameters are discussed in this pra
6、ctice.1. Scope1.1 This practice covers procedures for preparing pressedpowder transfer standards. These standards can be used in thenear-ultraviolet, visible and near-infrared region of the electro-magnetic spectrum. Procedures for calibrating the reflectancefactor of materials on an absolute basis
7、are contained in CIEPublication No. 44 (2). Pressed powder standards are used astransfer standards for such calibrations because they have ahigh reflectance factor that is nearly constant with wavelength,and because the geometric distribution of reflected flux re-sembles that from the perfect reflec
8、ting diffuser.1.2 The values stated in SI units are to be regarded as thestandard. The values in parentheses are for information only.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 esta
9、blish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:3E 284 Terminology of Appearance3. Terminology3.1 Terms and definitions in Terminology E 284 are appli-cable to this practice.3.2 Definitio
10、nsThe following definitions are particularlyimportant to this practice:3.2.1 perfect reflecting diffuser, nideal reflecting surfacethat neither absorbs nor transmits light, but reflects diffusely,with the radiance of the reflecting surface being the same for allreflecting angles, regardless of the a
11、ngular distribution of theincident light. (1990)3.2.2 reflectance, r, nratio of the reflected radiant orluminous flux to the incident flux in the given conditions.CIEA3.2.3 The term reflectance is often used in a general sense oras an abbreviation for reflectance factor. Such usage may beassumed unl
12、ess the above definition is specifically required bythe context. (1989b)1This practice is under the jurisdiction of ASTM Committee E12 on Color andAppearance and is the direct responsibility of Subcommittee E12.02 on Spectro-photometry and Colorimetry.Current edition approved Sept. 1, 2006. Publishe
13、d September 2006. Originallyapproved in 1965. Last previous edition approved in 2003 as E 259 98 (2003).2The boldface numbers in parentheses refer to the list of references at the end ofthis practice.3For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Servic
14、e at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.3.2.4 reflectance factor, R, nratio of the flu
15、x reflectedfrom the specimen to the flux reflected from the perfectreflecting diffuser under the same geometric and spectralconditions of measurement. CIEB(1988)4. Summary of Practice4.1 Procedures are given for the preparation of whitereference standards of diffuse reflectance factor and diffuserad
16、iance factor. The recommended materials are white powdersthat are pressed into plaques. These plaques provide closeapproximations to the optical properties of the perfect reflect-ing diffuser, and may be used to transfer a scale of absolutereflectance to another material or to an instrument.5. Signi
17、ficance and Use5.1 All commercial reflectometers measure relative reflec-tance. The instrument reading is the reflectance factor, the ratioof the light reflected by a reference specimen to that reflectedby a test specimen. That ratio is dependent on specificinstrument parameters.5.2 National standar
18、dizing laboratories and some researchlaboratories measure reflectance on instruments calibratedfrom basic principles, thereby establishing a scale of absolutereflectance as described in CIE Publication No. 44 (2). Thesemeasurements are sufficiently difficult that they are usually leftto laboratories
19、 that specialize in them.5.3 A standard that has been measured on an absolute scalecould be used to transfer that scale to a reflectometer. Whilesuch procedures exist, the constraints placed on the mechanicalproperties restrict the suitability of some optical properties,especially those properties r
20、elated to the geometric distributionof the reflected light. Thus, reflectance factor standards whichare sufficiently rugged and able to be cleaned, depart consid-erably from the perfect diffuser in the geometric distribution ofreflected radiance.5.4 The geometric distribution of reflected radiance f
21、rom apressed powder plaque is sufficiently diffuse to provide adependable calibration of a directional-hemispherical reflecto-meter. Although pressed powder standards are subject tocontamination and breakage, the directional-hemispherical re-flectance factor of pressed powder standards can be suffic
22、ientlyreproducible from specimen to specimen made from a given lotof powder, so as to allow one to assign absolute reflectancefactor values to all the powder in a lot.5.5 This practice describes how to prepare white reflectancefactor standards from a powder in a manner that allows astandardizing lab
23、oratory to assign the absolute scale of reflec-tance to the plaque.6. Apparatus6.1 The basic apparatus for producing a pressed powderstandard includes a powder press, powder containers and abalance. There are currently two commercial suppliers ofpowder presses. The press and receptacles can also be
24、made ina local machine shop. A suggested configuration is shown inFig. 1. The optical surface of the plaque should be pressedagainst a surface of ground glass or poly(methyl methacrylate)to provide a matte finish on the pressed plaque. Powderreceptacles should be at least 5 mm deep for BaSO4and at l
25、east10 mm deep for PTFE.7. Reagents and Materials7.1 Barium Sulfatethe barium sulfate should be of thehighest purity. It should be specially refined for optical andspectroscopic use (3).7.2 Polytetrafluoroethylenethe PTFE (4) should also bespecially refined for optical and spectroscopic use but some
26、commercial grades have been found to be acceptable substi-tutes. (5) Large quantities (drums) of commercial grade PTFEcan be obtained from manufacturers.8. Procedure8.1 Store all powdered reflectance standards in tightlycapped glass containers. If the powder is purchased in plasticcontainers, transf
27、er it to a glass container as soon as possible.Before using the powder, place it in a glass blender equippedwith stainless-steel or PTFE-coated blades and pulverize to auniform consistency. Transfer the quantity of powder to beused with stainless steel or PTFE-coated spoons. Perform thewhole operati
28、on in a draft-free location, away from sources ofsmall particulate contamination, filters, sweaters, windows,ovens, etc. Perform all measurements (weight, height, width,depth, volume, area, etc.) with adequate precision to ensurethat the final density is within 5 % of the specified value. Themost re
29、producible standards are made by pressing the powderto a specific density. Thus, determine the mass of the powder tobe used from the volume of the receptacle.8.2 Barium SulfatePress BaSO4to a density of 2000kg/m3(2.0 gm/cm3) and a thickness of at least 5 mm. Pressseveral specimens in succession. Sel
30、ect matched pairs to berepresentative of the contents of the bottle of powder. Keep thepressed plaques in a covered desiccator when not in use. Somesuppliers of BaSO4provide calibration values with each bottleof powder, other suppliers provide only 3 or 4 quality referencechecks and a reference to p
31、ublished values of referencestandards prepared from the powder. Table 1 gives the 6/diffuse reflectance factor values for EastmanWhite ReflectanceStandard (3).8.2.1 Another description of this procedure is found in Ref.(4).NOTE 1The collar and receptacle should be securely held in placebefore pressi
32、ng the powder.FIG. 1 Example Powder PressE2590628.3 PolytetrafluoroethylenePress PTFE to a density of1000 kg/m3(1.0 gm/cm3) and a thickness of at least 10 mm.The spectral reflectance, which is a function of density, has abroad maximum near this density. Prepare several specimens insuccession. Matche
33、d pairs are selected to be representative ofthe contents of the container of powder. Keep the pressedplaques in a desiccator when not in use. PTFE has a highdielectric constant and can be very sensitive to airborneparticulates. Such contamination can make the material slightlyfluorescent and reduce
34、its reflectance in the near-ultravioletspectral region. Table 2 lists the 6/diffuse reflectance factorvalues (6) and Table 3 lists the 45/0 reflectance factor values(7) of PTFE as determined by the National Institute ofStandards and Technology (NIST).9. Precision and Bias9.1 The National Institute o
35、f Standards and Technology andthe Inter-Society Color Council Project Committee 22, Mate-rials for Instrument Calibration, have carried out collaborativetests to determine the precision and bias of the preparation ofPTFE reflectance factor standards (8). The standard deviationof three determinations
36、 of the reflectance factor of PTFE by theNISTranged from 0.0002 to 0.0008 over the spectral range 300to 1000 nm. The measured reflectances of PTFE from twomanufacturers exhibited differences of from 0.002 to +0.004over the same range with the largest differences near the endsof the range and a const
37、ant measurement uncertainty of6 0.005. From the 9 laboratories participating in the round-robin experiment, 17 specimens were returned. The results areshown in Table 4 for the wavelength range 300 to 1000 nm.TABLE 1 6/Diffuse Reflectance Factor of Eastman WhiteReflectance Standard Pressed BaSO4Powde
38、rAWavelength, nm Reflectance Factor300 0.968350 0.979400 0.987450 0.991500 0.991550 0.992600 0.992650 0.992700 0.992750 0.992800 0.992850 0.991900 0.990950 0.9881000 0.986ADensity = 2000 kg/m3and thickness = 5 mm.TABLE 2 6/Diffuse Reflectance Factor of Pressed PTFEPowderAWavelength, nm Reflectance F
39、actorB300 0.984350 0.990400 0.993450 0.993500 0.994550 0.994600 0.994650 0.994700 0.994750 0.994800 0.994850 0.994900 0.994950 0.9941000 0.994ADensity = 1000 kg/m3and thickness $ 5 mm.BAccurate to 60.002.TABLE 3 45/0 Diffuse Reflectance Factor of Pressed PTFEPowderAWavelength, nm Reflectance FactorB
40、380 1.002390 1.003400 1.005410 1.006420 1.006430 1.007440 1.007450 1.008460 1.008470 1.009480 1.009490 1.009500 1.010510 1.010520 1.010530 1.010540 1.011550 1.011560 1.011570 1.011580 1.011590 1.011600 1.011610 1.011620 1.012630 1.012640 1.012650 1.012660 1.012670 1.012680 1.012690 1.012700 1.012710
41、 1.013720 1.014730 1.015740 1.015750 1.016760 1.016770 1.017ADensity = 1000 kg/m3and thickness $ 5 mm.BAccurate to 60.003.TABLE 4 Average and Standard Deviation of 6/DiffuseReflectance Factors of 17 PTFE Plaques Prepared by 9LaboratoriesWavelength, nmReflectance FactorAverageAStandardDeviationB300 0
42、.9792 0.0063350 0.9883 0.0021400 0.9911 0.0018500 0.9919 0.0020600 0.9915 0.0023700 0.9914 0.0023800 0.9912 0.00241000 0.9910 0.0024AAverage Density = 926.2 kg/m3.BStandard Deviation = 85.7 kg/m3.E2590639.2 The National Institute of Standards and Technologycarried out collaborative tests to determin
43、e the uncertainties inthe preparation of PTFE for use as transfer standards ofreflectance factor for the 45/0 geometry. Duplicate pressingswere made of the same PTFE in ten different laboratories. Thestandard deviations of the measured reflectance factor, as afunction of wavelength is shown in Table
44、 5. Table 6 shows themeasured reflectance factors, averages, and standard deviationsof four different drums of PTFE. The total uncertainty for thetransfer is approximately 1 % at wavelengths above 500 nmand approximately 1.5 % at wavelengths below 500 nm in thevisible spectral region.10. Keywords10.
45、1 bidirectional optical measuring system; hemisphericaloptical measuring system; integrating sphere; material stan-dards; reflectance and reflectivity; transfer standardsTABLE 5 Difference From the Average of PTFE Powder Pressings Ten Laboratories (A-J) and Two Replicates (1-2)Wavelength, nm380 450
46、600 700 770A1 0.002 0.004 0.002 0.003 0.004A2 0.004 0.006 0.003 0.001 0.003B1 -0.001 0.001 0.000 0.000 -0.007B2 -0.005 0.000 -0.001 0.000 -0.001C1 0.009 0.006 0.004 0.004 0.005C2 -0.005 -0.005 -0.004 -0.006 -0.005D1 0.001 0.002 0.001 0.001 0.002D2 0.007 0.004 0.003 0.002 0.002E1 -0.003 0.002 0.002 0
47、.003 0.004E2 -0.004 -0.004 -0.005 -0.006 -0.006F1 0.000 -0.011 -0.004 0.008 0.004F2 -0.001 0.000 0.001 0.001 0.001G1 -0.002 -0.004 -0.004 -0.004 -0.005G2 0.009 0.005 0.002 0.002 0.004H1 -0.012 -0.006 -0.006 -0.008 -0.007H2 0.010 0.001 0.000 0.001 0.002I1 -0.003 0.000 -0.002 -0.001 0.000I2 0.006 -0.0
48、02 0.002 0.002 0.005J1 -0.010 -0.007 -0.005 -0.007 -0.004J2 0.003 0.007 0.006 0.008 0.006Standard Deviation (k=2) 0.012 0.010 0.006 0.008 0.008TABLE 6 45/0 Reflectance Factor of Pressed PTFE Powder From Different Drums of PTFEWavelength, nm380 420 470 550 630 700 770Drum 1 1.005 1.008 1.011 1.013 1.
49、012 1.013 1.016Drum 2 1.001 1.006 1.009 1.011 1.012 1.012 1.017Drum 3 0.993 0.999 1.006 1.007 1.010 1.011 1.016Drum 4 1.007 1.010 1.011 1.012 1.013 1.013 1.017Mean 1.002 1.006 1.009 1.011 1.012 1.012 1.017Standard Deviation 0.013 0.010 0.008 0.005 0.002 0.002 0.001E259064REFERENCES(1) Publication CIE No. 46A Review of Publications on Properties andReflection Values of Material Reflection Standards, available fromUSNC/CIE. Request ordering information from Secretary USNC,NIST, Room A317/220, Gaithersburg, MD 20899.(2) Publication CIE No. 44Absolute Method
