Smithers optical and color testing expertise includes:
These methods are typically used to quantify changes in palstic materials after accelerated aging (UV exposure and weathering
and fluids testing
) or abrasion testing
Color measurements of polymer materials are assessed against the CIE L*a*b* scales which attributes numerical values to color and therefore allows easy comparison of colors and/or color change.
As detailed in the diagram below, the L-scale measures light vs dark, with the a-scale measuring red vs. green and the b-scale measuring yellow vs. blue.
Common standards for color testing:
- BS ISO 4582 Plastics. Determination of changes in color and variations in properties after exposure to glass-filtered solar radiation, natural weathering or laboratory radiation sources
- BS 3900-D8 (ISO 7724-1 withdrawn) Method of test for paints. Optical tests on paint films – Determination of color and color difference: principles
- BS 3900-D9 (ISO 7724-2 withdrawn) Method of test for paints. Optical tests on paint films – Determination of color and color difference: measurement
- B3900-D10 (ISO 7724-3 withdrawn) Method test for paints. Determination of color and color difference: calculation
- ASTM D2244 – Standard Practice for Calculation of Color Tolerances and Color Differences from Instrumentally Measured Color Coordinates
Greyscale color change testing
Color change can also be assessed using the Grey Scale. The essential scale consists of five pairs of non-glossy grey color chips (or swatches of grey cloth) which illustrate the perceived color differences corresponding to fastness ratings 5, 4, 3, 2 and 1. In addition, an augmented scale includes four half-steps for further refinement into nine steps.
Common standards for greyscale testing:
- BS EN ISO 105-A02:1993 Textiles. Tests for color fastness - Part A02: Grey scale for assessing change in color
Haze and transmission testing
Haze is the scattering of light as it passes through a transparent material. Haze measurements are most commonly made by the use of a spherical hazemeter. A spectrophotometer may be used which can provide valuable diagnostic data on the origin of the haze. The spectrophotometer fitted with an integrating sphere enables haze versus wavelength graphs or percentage transmission versus wavelength to be generated. For further details on spectrophotometer haze measurement.
Common standards for haze and transmission testing:
- ASTM D1003-Standard Test Method for Haze and Luminous Transmittance of Transparent Plastics – Procedure A (spherical hazemeter) & Procedure B (spectrophotometer)
- BS EN ISO 13468-1 Plastics. Determination of the total luminous transmittance of transparent materials. Single-beam instrument.
Specular gloss is a measure of how reflective a material is at a specified angle based on refractive index. Tests are carried out at different angles of reflection. 60° is the most common angle with lower angles (20°) used for high gloss samples and higher angles (85°) for low gloss samples.
Common standards for gloss testing:
- ASTM D523 Standard Test Method for Specular Gloss
- ASTM D2457 Standard Test Method for Specular Gloss of Plastic Films and Solid Plastics