ASTM D4303 is the standard test method for light resistance of colorants used in artist materials. It is used to approximate the color change over time of pigments used in an artist’s painting in an indoor exposure.
Use and factors to consider
The importance of retaining the color characteristics of pigments over a long period of time to an artist’s painting goes without saying. The color changes that can occur as a result of accelerated exposure are the result of long-term indoor lighting, so inform producers and user artists of the appropriate pigments for the paint. A color measurement, such as ASTM D2244, is taken on the sample before exposure and then compared to the reading after exposure.
ASTM D4303 tests expose samples to daylight filtered through a single-strength window glass or laboratory test source to accelerate the simulation of the effects of indoor exposure, using at least two of the four methods covered by ASTM D4303. These test methods are suitable for oils, resin oils, acrylics, emulsions, alkyd resins, watercolors, and gouache pigments, and are based on xenon arcs and fluorescent light sources.
Typical experimental parameters for ASTM D4303 tests
ASTM D4303-16 Standard Test Method for Light Resistance of Colorants in Artist Materials
Test method A.
Exposure: Natural sunlight filtered through glass
Total spectral radiation exposure: should be specified, but is usually 1260 MJ/m 2
Test method B.
Exposure: The irradiance of a daylight fluorescent lamp
Light/dark cycle time: to be specified
Total spectral radiation exposure: should be specified, but is usually 1260 MJ/m 2
Test duration: 9 months
ASTM D4303-16 Standard Test Method for Light Resistance of Colorants in Artist Materials
Test method C.
Exposure: Xenon arc irradiance simulates sunlight filtered through glass
Radiation exposure (at 340nm) : specified, but usually 1260MJ/m 2
Irradiance: specified, but usually 0.35 W / 2 / nm
Relative humidity: Needs to be specified, but is usually 55± 5%
Black Panel temperature: This parameter is required
Dry bulb temperature: To be specified
Panel rotation schedule: To be specified
Exposure period: specified
Test method D.
Exposure: The irradiance of very high output cold white fluorescent lamps and the indirect exposure of sodium-calcium glass filtered fluorescent UV sunlamps represent lighting in indoor environments
Initial Cold White (CW) UV irradiance in W/m2: Should be specified
Final CW UV irradiance in W/m2: will be specified
Initial fluorescent sunlamp (FS) UV irradiance W/m2: will be specified
Final FS UV irradiance in W/m2: should be specified
Panel rotation schedule: To be specified
Oil, resin oil, and acrylic emulsion paint samples need to be exposed by test methods A and B, C, or D, while watercolors, gouache, and other water-sensitive paints need to be exposed to test methods C and B or D.