5.1 The retention of chromatic properties by a colorant over a long period of years is essential in a work of art. Accelerated exposure simulates color changes that may reasonably be expected. The producer and the user of artists' materials, therefore, can be apprised of suitable colorants.

5.2 Variations in results may be expected between the test methods. Also, some variation may be expected when the same test is repeated. Variations in Methods A and B are due to differences in outdoor conditions that are not accounted for in testing to equivalent radiant exposures. Information on sources of variability and strategies for addressing variability in laboratory accelerated exposure tests is found in Guide G141.

5.3 This standard does not cover factors other than lightfastness that can affect the permanence of art materials.

1.1 Four test methods to accelerate the effects of long term indoor illumination on artists’ materials are described below. One of the natural daylight methods and one of the xenon-arc methods are used to categorize the lightfastness of colorants.

1.2 These test methods are used to approximate the color change that can be expected over time in colorants used in artists' materials exposed indoors to daylight through window glass.

1.3 Lightfastness categories are established to which colorants are assigned based on the color difference between specimens before and after exposure.

1.4 Color difference units are calculated by the CIE 1976 L*a*b* color difference equation.

1.5 These test methods apply to colored artists’ materials.

1.6 The values stated in SI units are to be regarded as the standard. The values given in parentheses are for information only.

1.7 This standard does not purport to address the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.