ASTM D523-14 pdf free download.Standard Test Method for Specular Gloss.
3. Terminology
3.1 Definitions:
3. 1.1 relative luminous reflectance factor, n—the ratio of the luminous flux reflected from a specimen to the luminous flux reflected from a standard surface under the same geometric conditions. For the purpose of measuring specular gloss, the standard surface is polished glass.
3.1.2 specular gloss, ui—the relative luminous reflectance factor of a specimen in the mirror direction.
4. Summary of Test Method
4.1 Measurements are made with 60, 20. or 85° geometry (8, 9). The geometry of angles and apertures is chosen so that these procedures may be used as follows:
4.1.1 The 60° geometry is used for intercomparing most specimens and for determining when the 20° geometry may be more applicable.
4.1.2 The 20° geometry is advantageous for comparing specimens having 60° gloss values higher than 70.
4.1.3 The 85° geometry is used for comparing specimens for sheen or near-grazing shininess. It is most frequently applied when specimens have 60° gloss values lower than 10.
5. Significance and Use
5.1 Gloss is associated with the capacity of a surface to reflect more light in directions close to the specular than in others. Measurements by this test method correlate with visual observations of surface shininess made at roughly the corresponding angles.
5.1.1 Measured gloss ratings by this test method are obtained by comparing the specular reflectance from the specimen to that from a black glass standard. Since specular reflectance depends also on the surface refractive index of the specimen. the measured gloss ratings change as the surface refractive index changes. In obtaining the visual gloss ratings, however. it is customary to compare the specular refleciances of two specimens having similar surface refractive indices.
5.2 Other visual aspects of surface appearance, such as distinctness of reflected images, reflection haze, and texture, are frequently involved in the assessment of gloss (1), (6), (7). Test Method E430 includes techniques for the measurement of both distinctness-of-image gloss and reflection haze. Test MeDiod 1)4039 provides an alternative procedure for measuring reflection haze.
5.3 Little information about the relation of numerical-to- perceptual intervals of specular gloss has been published. However, in many applications the gloss scales of this test method have provided instrumental scaling of coated specimens that have agreed well with visual scaling (10).
5.4 When specimens differing widely in perceived gloss or color, or both, are compared, nonlinearity may be encountered in the rclationship between visual gloss difference ratings and instrumental gloss reading differences.ASTM D523 pdf download.