Astm stp 478 1970

APPEARANCE OF METALLIC SURFACES A symposium presented at the Seventy-first Annual Meeting AMERICAN SOCIETY FOR TESTING AND MATERIALS San Francisco, Calif., 23-28 June 1968 ASTM SPECIAL TECHNICAL PUBLICATION 478 List price $7.00 Copyright by ASTM Int'l (all rights reserved); Fri Jan 22:58:10 EST 201 AMERICAN SOCIETY FOR TESTING AND MATERIALS Downloaded/printed by 1916 Street,(University Philadelphia, Pa 19103pursuant to License Ag University of Race Washington of Washington) Ó BY AMERICAN SOCIETY FOR TESTING AND MATERIALS 1970 Library of Congress Catalog Card Number: 77-132803 ISBN 0-8031-0065-5 NOTE The Society is not responsible, as a body, for the statements and opinipns advanced in this publication Copyright by ASTM Int'l (all rights reserved); Fri Jan 22:58:10 EST 2016 Downloaded/printed by Printed in Baltimore, Md University of Washington (University of Washington) pursuant to License Agreement No further October 1970 Foreword The Symposium on Appearance of Metallic Surfaces was presented at the Seventy-first Annual Meeting of the American Society for Testing and Materials held in San Francisco, Calif., 23-28 June 1968 The sponsor of this symposium was Committee E-12 on Appearance of Materials E F Barkman, Reynolds Metals Co., presided as symposium chairman In addition to the four papers presented at the symposium a paper by B W Robinson has been included in this publication Copyright by ASTM Int'l (all rights reserved); Fri Jan 22:58:10 EST 2016 Downloaded/printed by University of Washington (University of Washington) pursuant to License Agreement No f Related ASTM Publications Stainless Steel for Architectural Use, STP 454 (1969), $9.75 Nomenclature and Definitions Applicable to Radiometric and Photometric Characteristics of Matter, STP 475 (1970), $3.00 Copyright by ASTM Int'l (all rights reserved); Fri Jan 22:58:10 EST 2016 Downloaded/printed by University of Washington (University of Washington) pursuant to License Agreement No furt Contents Introduction Appearance Attributes of Metallic Surfaces—R s HUNTER Measurement of Appearance Characteristics of Stainless Steel—A E GLUBISH 22 Specular and Diffuse Reflectance Measurements of Aluminum Surfaces— E F BARKMAN 46 Instruments for the Measurement of Metallic Appearance—J s CHRISTIE 59 Proposed Method of Measurement for Appearance of Rolled Aluminum Surfaces Using Distinctness of Image and Diffuse Reflectance Measuring Instruments—B w ROBINSON 79 Copyright Downloaded/printed University by by of This page intentionally left blank Copyright by ASTM Int'l (all rights reserved); Fri Jan 22:58:10 EST 2016 Downloaded/printed by University of Washington (University of Washington) pursuant to License Agreement No further reprodu Introduction For the past several years, ASTM Committee E-12 on Appearance of Materials has been studying the appearance of metallic surfaces This work has been conducted by Task Group The participants in this work soon realized that there existed no adequate and comprehensive compilation of techniques for describing the appearance attributes of metallic surfaces Other materials have long been studied with respect to their appearance For example, the color, texture, and visual appearance of white and colored textiles, papers, and paints have been well defined, and ASTM test methods for measuring chromatic attributes and gloss can be found in the Book of Standards The metallic surfaces, however, presented a uniquely different problem of measuring the appearance Most metallic surfaces have very little or no chromatic attributes Or at least the chromatic features are not of major importance to describe the visual properties of metals Instead, metals exhibit the features which the consumer generally refers to as "brightness." This term, which is somewhat of a misnomer for describing what the eye first notices about metals, is one of the problems of accurate definitions confronting the workers in this field In the past several years the metallic appearance of bare and coated metal products has developed an increasingly larger importance to consumer products such as automotive and appliances Other product areas, such as jewelry and other decorative items, are examples where the metallic appearance is a primary characteristic of consumer appeal of the product The space age also introduced needs for measuring and defining the optical properties of metallic surfaces as related to reflectors, surfaces to provide thermal balance in space vehicles, and the characteristics of metallic surfaces with respect to electromagnetic radiation and reflection outside the visible spectrum This publication, however, will present results and findings of workers who are primarily concerned with the materials most commonly used for consumer products such as aluminum and stainless steel It should be emphasized, however, that the discussions on the appearance and measurement of metallic surfaces, though giving heavy emphasis to aluminum and stainless steel can be applied usually to other metals such as plated coatings (whether on metal or plastic substrates) including chromium, nickel, and silver, and any other metal surface where it is desirable to describe the metallic appearance Chromatic attributes of metallic surfaces are not described in this publi1 APPEARANCE OF METALLIC SURFACES cation First, the techniques for measuring chromatic attributes using such well-developed systems as the CIE and others can be regarded as applicable to metallic surfaces with one very important qualification If the metallic surface is nearly totally mat or diffuse, such as a mat-gold surface, the methods for measuring chromatic attributes or color on other materials can be used If, however, the metallic surface has some measure of distinctness of image or mirror qualities, the question whether the chromatic attributes should be measured on the specular or the diffused portions must be answered An extreme approach to this has been proposed, including the application of a diffuser filter over the specular metallic surface and measuring the chromatic attributes on the reflected and fully diffuse portion of the light This publication represents the experiences and findings of some of the country's foremost authorities in the field of reflectance measurements on metallic surfaces No other publication has covered this subject as thoroughly in these areas as does this compilation of papers The original symposium contained four papers to which has been added the paper by B W Robinson These papers cover the use of the principal instrumental techniques that have proven useful in measuring metallic surfaces in the research laboratories and in production environments This book should prove extremely valuable to those who have a need for measuring or specifying products where the metallic finish is of primary importance E F Barkman Director, Applied Chemistry and Mathematics, Metallurgical Research Division, Reynolds Metals Co., Richmond, Va 23219; symposium chairman Copyright by ASTM Int'l (all rights reserved); Fri Jan 22:58:10 EST 2016 Downloaded/printed by University of Washington (University of Washington) pursuant to License Agreement No further r R S Hunter1 Appearance Attributes of Metallic Surfaces REFERENCE: Hunter, R S., "Appearance Attributes of Metallic Surfaces," Appearance of Metallic Surfaces, ASTM STP 478, American Society for Testing and Materials, 1970, pp 3-21 ABSTRACT: The appearance of bare and finished metal surfaces is becoming more important, especially to the automotive and architectural fields The metals industry, however, is behind the paint, plastics, and paper industries in the development of methods for instrumental appearance measurements of metal products Metals are optically different from nonmetals because of free electron movement, and thus nonmetal measurement techniques are not generally applicable A complete analysis of metallic appearance requires complex combinations of spectrophotometric and goniophotometric curves By isolating attributes which can be related directly to observed appearance and correlated with physical properties, simpler instrumental measurement techniques can be developed These attributes can be divided arbitrarily into color and geometric attributes As described in this paper, the color attributes of metallic appearance are shininess, hue, and saturation The geometric attributes are haze, distinctness of image, luster, surface texture, and directionality KEY WORDS: metallic appearance, gloss, metals, brightness, surface properties, goniophotometers, reflection, evaluation, tests Bare metal surfaces are harder to measure for specific appearances than are nonmetal surfaces of paint, paper, plastic, and the like This is because of the variety of geometric distributions of reflected light associated with metallic appearance Although measurements are not in general use, appearance is commercially important for metallic surfaces used in automotive trim, bus and truck paneling, architectural metals, and decorative and costume jewelry The present paper identifies six different methods of evaluating reflected light for correlation with six geometric attributes of appearance Appearance and the Metals Industry Whenever a product has a metallic surface exposed to observation by the human eye, the appearance of that surface has economic importance President, Hunter Associates Laboratory, Inc., Fairfax, Va 22030 72 APPEARANCE OF METALLIC SURFACES FIG 9—Drawing of optical head of the photovolt reflectometer specular reflectance correspond to fine texture It should be noted that he is able to measure surface texture in this manner only because the waves in the surfaces of most aluminum specimens have specific orientation It is possible that his method would fail on some roll or mold-textured surfaces Perhaps Robinson's most important contribution for success of measurements of metallic appearance was the development of devices for flattening and holding sheets of metal and foil flat during measurement Figure 11 Copyright by ASTM Int'l (all rights reserved); Fri Jan 22:58:10 EST 2016 showsDownloaded/printed the type specimen holder which Robinson designed for metals With by University of Washington (University of Washington) pursuant to License Agreement No further rep CHRISTIE ON MEASUREMENT OF METALLIC APPEARANCE 73 FIG 10—Optical diagram of Hunterlab D36 distinctness-of-image glossmeter the lever arm and flat metal plate, Robinson is able to apply strong flattening pressures to sheets of metal which may have curvature from coil set or from other causes In the photograph, the lever arm used to apply pressure to specimens can be seen It also can be seen that the whole combination of specimen, clamp, and jig which fits into the glossmeter can be rotated This opportunity to rotate the surface being tested without removing it from the flattening clamp permits measurements of the same test area at the same flatness both in and across the coil direction A number of workers making measurements with the Hunterlab D36 distinctness-of-image glossmeter have found it difficult to obtain results which agree from one laboratory to another It is believed that a major source of these disagreements between laboratories have been the result of unsatisfactory panel flattening Robinson's panel clamp, which has also been used at Hunterlab, undoubtedly has been a major factor in his sucCopyright ASTM Int'linstrument (all rights reserved); Fri Jan 22:58:10 EST 2016 cessful use ofbythe D36 Downloaded/printed by University of Washington (University of Washington) pursuant to License Agreement No further reprod 74 APPEARANCE OF METALLIC SURFACES FIG 11—Photograph of Robinson's specimen clamp Hunterldb D47 DORIGON Glossmeter By comparison with the D36 instrument, the DORI and abridged goniophotometer development of Tingle and George offer two advantages: The DORI method of distinctness-of-image measurement requires only geometric adjustment during instrument calibration By contrast the D36 instrument requires both optical alignment and electrical linearity adjustments The Tingle-George DORI and abridged goniophotometer devices can be combined into a single instrument giving all the geometric attributes of metals except surface uniformity To take advantage of these features, the Hunter Associates Laboratory designed a metals glossmeter combining the functions of DORI with the ALCOA abridged goniophotometer By using newly developed optical Copyright by ASTM Int'l (all rights reserved); Fri Jan 22:58:10 EST 2016 fibers, it has been possible, in a single instrument, to achieve the high Downloaded/printed by University of Washington (University of Washington) pursuant to License Agreement No further CHRISTIE ON MEASUREMENT OF METALLIC APPEARANCE 75 resolving power necessary for the DORI image evaluation The same instrument, by means of additional fibers and receptor slits, measures specular reflectance, Rs, haze at and deg and diffuseness at 15 deg from the specular direction Figure 12 is an optical diagram of this new instrument VIEW A-A Copyright by ASTM Int'l (all rights reserved); Fri Jan 22:58:10 EST 2016 FIG 12—Optical diagram of the Hunterlab D^7 DORIGON glossmeter Downloaded/printed by University of Washington (University of Washington) pursuant to License Agreement No further 76 APPEARANCE OF METALLIC SURFACES which is called the Hunterlab D47 DORIGON glossmeter Note that this instrument also uses the Robinson panel clamp Distinctn ess-of-Image Comparison In Fig 13, curves have been plotted from distinctness of image data obtained on a series of specimens measured on the DORI, DIG, D36, and D47 instruments The close agreement in curve slope for the three abridged instruments shows that specimens with small differences in distinctness of image would be assigned values with relatively uniform numerical correlation over most of the scale The D10 data included in the graph were obtained using extremely narrow field angles and a different method of computation Because of this, differences between high distinctness of image specimens are reduced On the graph, this condition is indicated by the more gradual slope at the top of the D10 curve FIG.Copyright 13—Comparison of distinclness-of-image curves for Fri specimens measured on D10, by ASTM Int'l (all rights reserved); Jan 22:58:10 EST 2016 DORI,Downloaded/printed D36, and Dtf instruments by University of Washington (University of Washington) pursuant to License Agreement CHRISTIE ON MEASUREMENT OF METALLIC APPEARANCE 77 FIG 14—Diagram of Hunterlab D16 Glossmeter beams used for ^5-deg specular gloss and ^5, —^5/^5, —20-deg contrast luster Hunterlab D16 Glossmeter One other instrument which has been used for haze and specular gloss measurements is the Hunterlab D16 multiangle glossmeter The geometric diagram of this instrument is showTi in Fig 14 This multipurpose glossmeter has been used with 20, 60, and 75 deg, as well as the 45-deg angle (shown) for specular reflectance With a or 20-deg viewing beam on the specular side (25 deg from the specular direction) determinations are made of the diffuse component By itself, this diffuse component is used to measure haze or diffuseness Compared with specular reflectance, it also provides luster or contrast-gloss measurements Directionality can be measured by change in haze with panel orientation (Gh) for bright metals or contrast luster (Cc) for diffuse metals Surface Uniformity This attribute is important for metallic appearance, but up to now direct measurements have not been available As was noted above, Robinson found correlation between surface waviness of his aluminum panels and change of D36 instrument peak and slope readings with panel orientation He was successful in this effort because the D36 instrument uses a slit shaped light source and because the waves in the panels with which he ASTM Int'l (all rights reserved); Fri Jan 22:58:10 EST 2016 was Copyright working by were highly oriented with the grain of the metal Downloaded/printed by University of Washington (University of Washington) pursuant to License Agreement No furth 78 APPEARANCE OF METALLIC SURFACES Conclusion Although the metals industry is behind industries such as paint and paper in the acceptance of appearance measurements, there are a number of instruments available to assist the metals technologist in the identification of metallic appearance None of these instruments can describe completely the appearance of a given surface If, however, the metals qualitycontrol technologist visually can identify the attributes or attributes that are of importance to his product, he usually can select the appropriate instrument or instruments needed to meet his measurement problem References [1] Hunter, R S., "Methods of Determining Gloss," Journal of Research, National Bureau of Standards, RP958, Vol 18, No 1, Jan 1937 [2] Hunter, R S., "Gloss Evaluations of Materials," ASTM Bulletin, No 186, Dec 1952 [3] Hunter, R S., "Methods for Evaluating the Gloss of Ink Films," Journal, Technical Association of the Pulp and Paper Industry, Vol 46, No 7, July 1963 [4] Barkman, E F., "Specular and Diffuse Reflecting Characteristics," Metallurgical Research Report, 571-13A, Reynolds Metals Company, April 1959 [5] Tingle, W H and George, D J., "Measuring Appearance Characteristics of Anodized Aluminum Automotive Trim," Report 650513, Society of Automotive Engineers, May 1965 [6] Tingle, W H and Potter, F R., "New Instrument Grades for Polished Metal Surfaces," Product Engineering, 27 March 1961 Copyright by ASTM Int'l (all rights reserved); Fri Jan 22:58:10 EST 2016 Downloaded/printed by University of Washington (University of Washington) pursuant to License Agreement No further B W Robinson1 Proposed Method of Measurement for Appearance of Rolled Aluminum Surfaces Using Distinctness of Image and Diffuse Reflectance Measuring Instruments Scope 1.1 This method provides values for four independently variable surface characteristics that can be used to describe precisely the appearance of rolled aluminum surfaces This method is applicable to finishes ranging from mill sheet to luster sheet, from utility foil to decorative foil, as well as bright anodized surfaces.2 1.2 Color is not included as an appearance characteristic, nor are random surface defects identified using this method Summary of Method 2.1 In this method the four appearance characteristics are: (1) image clarity—(distinctness of image) (2) macrolinearity } \—(two independent directional features) (3) microlinearity J (4) whiteness—(haze) 2.2 Two instruments are used to obtain values for the four characteristics of appearance A Hunterlab distinctness-of-image glossmeter Model D36C3 provides measurements of 45 deg specular reflectance and image clarity Measurements are determined both parallel and at right angles to the rolling direction From these measurements values for image clarity, macrolinearity, and microlinearity are determined The fourth appearance characteristic, Alcan Canada Products, A Division of Aluminum Company of Canada, Ltd., Kingston,' Ont., Canada Robinson, B W., "A Method for Appearance Evaluation of Rolled Aluminum Surfaces," Metal Finishing, Vol 68, 1970, pp 45-52 Available from Hunter Associates Laboratory, Fairfax, Va., U.S.A 79 80 APPEARANCE OF METALLIC SURFACES FIG 1—Hunterlab D36 glossmeter Serial No (similar in operation to new D36C instrument) Copyright by ASTM Int'l (all rights reserved); Fri Jan 22:58:10 EST 2016 Downloaded/printed by University of Washington (University of Washington) pursuant to License Agreement No f ROBINSON ON PROPOSED METHOD OF MEASUREMENT 81 whiteness, is measured using a Canadian Research Institute reflection meter, Model CG-64 using with it a Model ARCT-AL search head A single measurement of diffuse reflectance provides the value for whiteness Significance 3.1 The appearance of rolled aluminum sheet and foil can be described quantitatively using this four parameter method 3.2 Appearance limits or tolerances can be established for each grade of finish 3.3 This method is applicable also to process capability studies and product development work, as well as for quality audit and control purposes Definition of Terms The name assigned to each appearance parameter was chosen to represent what one sees when visually appraising a surface The individual surface features identified in this method could be described with different names if necessary 4.1 Image Clarity—(distinctness of image) Denotes the clearness or distinctness of images reflected by a surface 4.2 Macrolinearity—The effect due to directional surface roughness caused by discontinuous long narrow ridges which blend into a fine pattern of waviness The presence of this characteristic is revealed where the outline of reflected images appears slightly torn or disturbed 4.3 Microlinearity—The effect due to a multitude of extremely fine striations or parallel lines oriented in the rolling direction The presence of this directional characteristic does not affect the outline of reflected images, and, although it is of a superficial nature, it is frequently a predominant visual characteristic 4.4 Whiteness—Indicates the degree of whitish haze or milkiness on a surface The presence of this characteristic does not affect the resolution or sharpness of image reflection, only the image contrast is reduced Apparatus 5.1 A Hunterlab Distinctness-of-Image Glossmeter Model D36C5 (see photograph Fig and diagram Fig 2) In this instrument, the Available from Canadian Research Institute, Don Mills, Ont., Canada A similar instrument is available from the Photovolt Corp., New York, N Y., U.S.A A necessary modification is described in 5.2 Only the recently redesigned Model D36C is suitable for this method Recent D36 Copyright by ASTMtoInt'l (all rights reserved); Fri Jan 22:58:10 EST 2016 models can be upgraded D36C condition by Hunterlab Downloaded/printed by University of Washington (University of Washington) pursuant to License Agreement No further 82 APPEARANCE OF METALLIC SURFACES A- Lamp B- Lens and Heat Filter C- Narrow Slit D- Projection Lens E- Specimen Surface F- Slit Disc G- Lens H- Filter I- Phototube FIG 2—Optical diagram of distinctness of image glossmeter reflected image of a narrow illuminated rectangular slit is allowed to fall on a rotating disk having a number of narrow radial slits which scan the reproduced image from side to side A phototube detects the light intensity as a function of the scanning position, and the peak intensity of light at the center of the image as a measure of specular reflectance The sharper the edges of the reproduced image the more sudden is the increase in reflected light intensity as the image is scanned An electrical circuit, by differentiation of the intensity scan, produces a direct readout of image clarity 5.2 A Canadian Research Institute Reflection Meter Model CG-6 used with a Model ARCT-AL diffuse search unit (see photograph Fig 3) provides a measurement of whiteness A diagram of the diffuse search unit is shown in Fig In this type of unit, light passes through two collimating lenses, a glass filter, and then through a central opening in a circular photocell, striking the specimen surface When nondirectional surfaces are measured, the specularly reflected light returns through the center of the photocell and is not recorded The remainder of the light, being rather uniformly diffusely reflected, is received by the photocell Rolled aluminum Copyright by ASTM Int'l (all reserved); Jan 22:58:10 EST 2016 surfaces, however, are rights seldom free Fri of directional textures, and Downloaded/printed by University of Washington (University of Washington) pursuant to License Agreement No fur ROBINSON ON PROPOSED METHOD OF MEASUREMENT 83 FIG 3—Canadian Research Institute reflection meter with specimen clamp in position on diffuse search unit Copyright by ASTM (all rights reserved); Fri Jansearch 22:58:10 FIG Int'l 4—Optical diagram of diffuse unit EST 2016 Downloaded/printed by University of Washington (University of Washington) pursuant to License Agreement No further 84 APPEARANCE OF METALLIC SURFACES these directional features cause strong reflected intensity in the diffuse region slightly off the specular position Since whiteness is represented by a measurement of uniformly scattered diffuse reflectance only, it is necessary to exclude these directional concentrations This is achieved by strip masking the face of the photocell, as illustrated in Fig This modification is identified by the addition of the letters AL to the ARCT model designation Standards and Standardization 6.1 The Hunterlab Model D36C glossmeter shall be supplied by the manufacturer with four calibrated standards of specular gloss and image clarity: (a) One front surface mirror of aluminum evaporated onto plate glass (b) Three intermediate testing standards at approximately 10, 45, and 75 on the image scale will be supplied in anodized aluminum The instrument shall be standardized according to the operating instructions supplied by the manufacturer 6.2 The Canadian Research Institute Model CG-6 instrument shall be supplied by the manufacturer with four calibrated master standards of whiteness (diffuse) These standards shall be supplied in anodized aluminum at approximately 25, 40, 60, and 75 on the whiteness scale The instrument shall be standardized according to the instructions supplied by the manufacturer for operation employing the scale expansion and zero suppression features of the instrument One high and one low standard is required for day to day calibration Operation 7.1 The Hunterlab Model D36C Glossmeter (a) Place specimen on rotatable specimen clamp with rolling direction parallel to light beam (6) Align specimen direction, use instrument meter deflection for greater accuracy (c) Clamp specimen—adjust specimen clamp pressure screw, if necessary, to achieve specimen flatness (d) Record specular reflectance value and image clarity value in the "with" rolling direction (e) Rotate specimen holder 90 deg (/) Record specular reflectance value and image clarity value in Copyright by ASTM Int'l (all rights reserved); Fri Jan 22:58:10 EST 2016 the "across" Downloaded/printed by rolling direction University of Washington (University of Washington) pursuant to License Agreement No further rep ROBINSON ON PROPOSED METHOD OF MEASUREMENT 85 7.2 The Canadian Research Institute Instrument Model CG-6—Following the operations described in 7.1, remove the specimen holder, (supplied with D36C instrument) with the specimen still in the clamped position, and place it over the measurement opening of the ARCT-AL diffuse search unit Rotate the clamped specimen until lowest meter indication is reached 7.3 Record this value as whiteness Computations 8.1 Compute average of "with" and "across" measurements of image clarity 8.2 Compute difference between "with" and "across" measurements of image clarity 8.3 Compute difference between "with" and "across" measurements of specular reflectance Report Values for three appearance characteristics, namely, microlinearity, macrolinearity, and image clarity are determined from The value for whiteness is derived from 7.3 9.1 Report average of "with" and "across" measurements of image clarity as image clarity 9.2 Report difference between "with" and "across" measurements of image clarity as macrolinearity 9.3 Report difference between "with" and "across" measurements of specular reflectance as microlinearity 9.4 Report measurement of whiteness from 7.3 Copyright by ASTM Int'l (all rights reserved); Fri Jan 22:58:10 EST 2016 Downloaded/printed by University of Washington (University of Washington) pursuant to License Agreement No