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History of 102-18 Dry-Wet Weathering Cycle

History of 102-18 Dry-Wet Weathering Cycle

Atlas SunSpots

Today I would like to share with you one entry from the very first edition of SunSpots back from 1972. If you recall, SunSpots was regularly published by Atlas, sharing technical articles, general information, and industry and company news. The last edition was circulated in 2016. For historical reference, issues nos. 61 to 99 are available in our online SunSpots archive.

The entry I found is interesting, but very telling as well. Early editions included a ‘question and answer’ series, and this issue addressed the question “How was the weathering cycle of 102-18 developed?”

How was the 102-18 Cycle Developed?

The wetting cycle in very early carbon arc weathering instruments, which has been used for over 70 years, is based on a cycle of 102 min light followed by 18 min of light with water spray. These early Atlas Sunshine Carbon Arc models came with a specimen rack that revolved once every 120 minutes and the spray was on continuously. With the continuous specimen spray, it was determined back then that it took about 18 minutes for a specimen to pass through the water spray. For the rest of the 2 hours, 102 minutes, the specimens were then considered to be dry.

Since first implemented, the 102-18 dry-wet cycle has been extremely popular, with remarkable global impact on weathering tests. A vast number of standardization committees adopted it, e.g., for polymer and coatings xenon test methods such as ISO 4892-2, ISO 16474-2, EN 513, and ASTM G155. Even some automotive standards such as Volkswagen’s PV 3930 or today’s textile weathering standard ISO 105-B10 include this cycle.

New Wetting Cycles

The 102-18 cycle was not developed to mimic a specific environment. However, modern test cycles such as the one used in the state-of-the-art automotive and aerospace test standard ASTM D7869 were developed by simulating the reference end use environment. In this case, the reference environment is a subtropical South Florida environment, and coincidentally, test results validate the effectiveness of the new cycle.

Another example is the US textile standard AATCC TM169-2020 which adds a 90-30 spray cycle for South Florida conditions.

Is the 102-18 cycle an effective cycle, or is it simply used because it has been there for such a long time? Well, that’s a good question that should be addressed in more detail another day.

More Information

Learn more about the major effects of weathering - radiation, heat, and water - in our recorded seminar Factors of Weathering.

Look up the development of the ASTM D7869 test method in our online seminar on Automotive Interior and Exterior Weathering and Lightfastness Testing.

Interested in weathering standards? Listen to the recorded seminar Weathering Test Methods And Basic Standards or check out our website.