Significance and Use 4.1 This specification establishes quality requirements and provides a basis for common understanding among producers, distributors, and users. 4.2 It is not intended that all pastels meeting the requirements be identical nor of uniform excellence in all respects. Variations in manufacture, not covered by this specification, may cause some artists to prefer one brand to another, either of which may be acceptable under this specification. 4.3 Variation in test results can be due to differences in pigment manufacture from time to time by a company, different properties of a pigment from company to company, different combinations of pigments and other ingredients, specimen preparation, thickness of pastel on substrate, different instruments and instrumental readings, variations in the surface of the specimen, and the conditions of exposure. Allowance for these variations is made by establishing lightfastness categories that include a range of color differences. 4.4 Since a specific pastel may be unusually sensitive to some aspect of simulated daylight accelerated lightfastness testing and show a change in color that would not occur in a normal home or gallery environment, two types of exposure are required, both natural daylight and simulated daylight. 4.5 Some variation in test results is to be expected even when the same type of exposure is repeated. Therefore, after triplicate specimens are exposed in each of the two types of exposures, the lightfastness category of the pastel by each exposure method is based on the mean of the color change of the three specimens, or two specimens if an outlier is discarded. 4.6 If the two methods place the pastel in the same lightfastness category, the pastel is assigned to that category. If the pastel is placed in different lightfastness categories by the two methods, either the pastel is placed in the poorer of the two categories or a retest is conducted using the test method that yielded the poorer lightfastness category. The lightfastness category by that test method is based on the mean of the color change of the specimens in both the original and retest that had not been discarded as outliers.Scope 1.1 This specification establishes requirements for composition, performance, and labeling of artists’ pastels. 1.2 This specification includes requirements for identification and lightfastness. 1.3 Pastel specimens are exposed to both natural daylight through window glass and window glass-filtered simulated daylight radiation to determine the lightfastness category for each pastel. 1.4 The values stated in SI units are to be regarded as standard. The values given in parentheses after SI units are provided for information only and are not considered standard. 1.5 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
