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Glossiness is evidenced by almost every object and is to be attributed to specular reflection. Specular reflection occurs at the surfaces of reflecting objects; and, because of the diversities of minute surface structure, many kinds of glossy appearance result. An attempt to classify these glossy appearances has led to the description of six different kinds of gloss: (1) specular gloss, identified by shininess; (2) sheen, identified by surface shininess at grazing angles; (3, contrast gloss, identified by contrasts between specularly reflecting areas of surfaces and other areas; (4) absence-of-bloom gloss, identified by the absence of reflection haze or smear adjacent to reflected high lights; (5) distinctness-of-reflected-image gloss, identified by the distinctness of images reflected in surfaces; and (6) absenceof-surface-texture gloss, identified by the lack of surface texture and surface blemishes.In describing the appearances of objects, one commonly distinguishes between the effects due to two types of reflection; glossiness, on the one hand, may be correlated with specular, or surface reflectance; the degree of lightness or darkness may, on the other hand, be correlated with diffuse reflectance usually occuring within the pigmented and scattering media beneath these surfaces. Specular reflection is evidenced by light preponderantly reflected in the direction of mirror reflection, whereas diffuse reflection is evidenced by light scattered in all directions by the reflecting object. Unfortunately for the purposes of gloss and reflectance measurement, the effects of specular reflection and diffuse reflection cannot be completely separated. The gloss of a surface cannot, in the general case, be defined in any simple way that permits quantitative measurement.Data which describe the directional distribution of light reflected by surfaces illuminated under specified conditions furnish the fundamental physical basis for describing gloss. However, such distribution data are cumbersome and involved and include the effects of both diffuse and specular reflection . It is because these goniophotometric (reflection distribution) data are unwieldy that, in the past, devices for measuring gloss have been developed by simple empirical means. By trial and error, methods have been found to measure the gloss of particular types of materials exhibiting particular types of gloss .The article suggests that the designer of a prospective gloss meter should determine from goniophotometric data taken on representative samples what differences in apparent reflectance are most characteristic of the differences in glossiness observed visually. That is, gloss-meter design will have considerably less of the trial-and-error element when goniophotometric data are used to indicate the most pertinent reflectance measurements to make for various purposes.Also included are descriptions of typical gloss instruments, descriptions of measurements they make, and a bibliography on gloss. Differences between the various types of gloss are analyzed i...

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To analyze appearance attributes optically, one first separates the chromatic attributes from the geometric ones. The chromatic, or color, attributes may be represented in a variety of forms which start with the purely physical spectrophotometric curves. By incorporating the sensory processes of the human observer, one converts spectrophotometric data to colorimetric specification by use of the CIE Standard Observer and Coordinate System. To obtain analyses which relate closely to the observer's sensory impressions, one can convert CIE specifications to one of several opponent-colors (L,a,b-type) analyses or to hue, value, and chroma of the Munsell-type analyses. These sensory-related color specification systems can be used to locate points representing colors in three-dimensional coordinate systems. Geometric attributes are those related to the geometric manners in which objects and materials distribute light and are known by terms such as gloss, turbidity, texture, and the like. Measurement methods for many of the various geometric attributes have been developed. Total instrumental analyses of the physical correlates of appearance are so complex that measurement is not feasible and is never attempted. There do exist, however, a large number of practical, useful methods for instrumentally measuring specific attributes of the appearance of materials. Many of these have been standardized in print by the American Society for Testing and Materials (ASTM), which now has the largest published collection of appearance analyses in existence. Although ASTM has accomplished much in promoting measurements of appearance attributes, there exist important requirements for test procedures not yet prepared. The technical state of the art has recently progressed so that ASTM should now be able to meet these unsatisfied requirements.

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The multipurpose reflectometer was developed primarily to measure apparent reflectance, specular gloss, and trichromatic coefficients. These meas urements are useful in the ceramic, paint, text ile, paper, and chemical industries to indicate lightness, gloss, and color of finished articles. I n the reflectometer, two light beams from a single source are directed along separate p aths to two barrier-layer photocells. Various types of these photocells were studied to find which could be used most advantageously. The reflectometer employs a s ubstitution null method and requires a galvanometer to indicate equality of the currents generated by the two photocells. For each sample tested, there is a photometric adjustment to restor e equality of the currents. The amounts of photometric adjustment are m easured on the direct-reading scales , one of which is used for apparent reflectance and the other for spec ul a r gloss. Because of its high precision, the instrument is well suited for measuring small differences in apparent reflectance, gloss, or color of nearly identical samples. However, for grea t est accuracy, it is necessary to correct the scale readings by calibration.