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Trust is Good – Control is Better: Validation of Weathering Reference Materials



Weathering Reference Materials

Back in the early days of lightfastness and weathering testing, there were only limited options for monitoring and controlling test parameters in natural and accelerated testing. For validating comparable testing between exposures, materials of known weathering performance – so called “weathering reference materials” were required.

Even though today we have elaborated methods to measure and control irradiance, air, surface temperature, and relative humidity, there can still be instrument to instrument variation. This is why the most important weathering standards such as the ISO 4892 and ISO 16474 series, and ASTM G151, G154 and G155 still recommend the use of reference materials.

In addition to the sensitivity to UV and light, some reference materials are also sensitive to temperature and moisture. Depending on the type and sensitivity of reference materials, they can be used to compare different exposures or to set the exposure duration, based upon a specific property change of the reference material. If inconsistencies are observed, reference materials can also be used for trouble shooting.

Most Frequently Used Reference Materials

The table and the image show the most important weathering and lightfastness reference materials and their specific sensitivities. These characteristics may be used singly or in combination to isolate problems and determine the cause of out-of-specification reference material testing results.





Lot-to-Lot Variation

Most weathering and lightfastness reference materials are produced, validated and distributed by national and international organizations and associations. However, even with the highest quality precautions, there might be lot-to-lot variation. Therefore each lot needs to be validated individually.

The ISO blue wool scale consists of eight types of blue wools (BW), each type with different lightfastness, with BW1 having the lowest and BW8 having the highest lightfastness. For the ISO blue wools there is a standard for the validation procedure (ISO 105-B08). However validation is only required to the test conditions described ISO 105-B02 (textile lightfastness). If you plan to use the ISO blue wools for other test methods and test conditions (for example hot-light fastness testing according to ISO 105-B06) you need to contact your reference material supplier for guidance.

AATCC (American Association of Textile Chemists and Colorists) performs validation testing for each lot of AATCC blue wool (currently only BW L2 is available). It is validated for AATCC TM16.3 (textile lightfastness). In cooperation with SAE (Society of Automotive Engineers) it is also validated for hot-light fastness testing according to SAE J2412. If you buy AATCC BW L2, it comes with a certificate and correlation data between color change and radiant exposure. Similar, each lot of SAE Polystyrene chips is validated for SAE J2527 (weathering) and SAE J2412 (hot-light fastness testing) and comes with a certificate and performance data.

Because of these potential lot-to-lot variations it is important not only to include the reference material description, but also its lot number into the test documentation. This often helps explain differences in test results from different instruments or laboratories.

More Information

You find more information in our recorded online seminars on
- Weathering reference materials
- Lightfastness testing of textiles
or in our Technical Guide on color measurement.

For further information have a look into our online library, listen to recorded online seminars or review upcoming online and on-site educational classes.