Measurement of sixty-degree specular gloss

Abstract

Specular gloss is the attribute next to color that is most often used in the evalua(,ion of the appearance of obj ect s. For 10 years t he American Society for T estin g N[a(,erials has used a method of test for the 60 0 specular gloss of pain t fini shes based on research done at this Bureau. The ASTM method prescribes the illuminator and receiver apertu res that are to be used. However, in order to determine the uncertain ties involved in the calibration of gloss standards, the rate of change of gloss reading with change of aperture was investigated throughout the gloss scale. Thi s was done by modifying an existing goniophotometer so that it became in effect a versatile glossmeter with provis ion for accuratcly controllin g all of the known geometrical vari ables involved. Data obtained on the variation of gloss readin g with aperture show that standards with widely different distr ibutions of re flected ligh t can be used to check t he adjustment of glossmeters and the conformance of thei r apertures to ASTM specifications in the in creasingly importan t medium-to highglos range. The problem of obtaining the d ir-ru e correction, which in vol ves sou ree polari zation and depart ure of the specimen from a pe rfect diffuso r, has been investigated.

Analysis of Goniophotometric Reflection Curves*

“…Figures in brackets indicate the literature references at the end of this paper 2. Photometric definitions and terms used here are contained in a paper by Hammond and Nimeroff[6].…”

Analysis of goniophotometric reflection curves

“…This curve sugges ted to him an analogy to the frequency distribut ion curve according to the law of probability. H e thell compu ted the dispersion index, u , (usually called s tandard deviation) using the r elation, (6) where e is the a ngle of tilt of th e specimen . This equation is analogous to taking the square root of eq (1), for which k = 2.…”

The Improvement of Luster of Cotton

“…These angles are measured from the &dquo;normal,&dquo; a line at right angles to the general surface of the specimen. The complete definition also needs to include the spread of the beams about the central rays [15], but this factor is considered later (p. 478) in examining the effect of experimental arrangements on the results.…”

“…The larger the area illuminated, the more the rays from the edge can depart from the direction of the central line and still pass from source to reflecting surface to receiver. This blurring by angular spread of rays will make more difference, the more rapidly the reflection characteristics change with angle-that is to say, the greater the contrast [15]. 2 The working arrangements in the variable-angle instrument are only partially indicated in the diagram in Figure 1.…”