What is the ASTM standard for lightfastness?

The ASTM standard for lightfastness is ASTM D4303 - Standard Test Methods for Lightfastness of Colorants Used in Artists' Materials. This standard provides guidelines for evaluating the lightfastness of colorants used in artists' materials, such as pigments, dyes, and inks. The purpose of this standard is to determine the resistance of these colorants to fading or color change when exposed to light.

ASTM D4303 includes several test methods that can be used to assess lightfastness, including:

1. Method A - Blue Wool Scale Method: This method involves exposing test specimens to a controlled light source and comparing the fading of the colorant to a set of blue wool standards. The blue wool standards have known lightfastness ratings, ranging from 1 (poor lightfastness) to 8 (excellent lightfastness).

2. Method B - Xenon-Arc Lamp Method: This method uses a xenon-arc lamp to simulate natural sunlight and exposes test specimens to this light source for a specified period. The fading of the colorant is then evaluated visually or instrumentally.

3. Method C - Carbon-Arc Lamp Method: This method uses a carbon-arc lamp to simulate sunlight and exposes test specimens to this light source for a specified period. The fading of the colorant is evaluated visually or instrumentally.

4. Method D - Fluorescent Lamp Method: This method involves exposing test specimens to fluorescent lamps that emit specific wavelengths of light. The fading of the colorant is evaluated visually or instrumentally.

ASTM D4303 provides detailed procedures for conducting these test methods, including sample preparation, exposure conditions, and evaluation criteria. It also provides guidance on reporting the lightfastness results.

It is important to note that ASTM D4303 is specifically focused on lightfastness testing for artists' materials. For other applications, such as textiles or industrial products, different ASTM standards may be applicable.