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Accelerated weathering correlation statements – A risky marketing strategy.

An initial enquiry for UV testing goes something like this:

Dear Accelerated Weathering Laboratory Ltd.

Our marketing department has requested our literature should state that our product is capable of withstanding 2 years outside exposure without significant fade. We believe our products are photo-stable over this period so we require an accelerated weathering test programme to prove this.

As 500 hours exposure is equivalent to 1 year outside, please would you quote us for 1000 hours exposure in accordance with BS EN ISO 4892 part 2. Your test report should state that our mouldings are photo-stable over a min period of 2 years if they have a dE shift less than 2.


Fudgit and Bodge Mouldings UK Ltd.


Now………. There are no short answers to this one without going into ‘geek mode’ so please accept my apologises and find the actual reply from AWL by return email below:


FAO Mr Fudge and Mr Bodge.

Thank you for your enquiry concerning accelerated weathering testing.

I am concerned you have made a definitive correlation statement regarding accelerated weathering tests and real time correlation.

At the set point irradiance level, BP temperatures and humidity levels of ISO 4892-2 I do not agree with the 500 hours = 1 year statement. Our experience with many different materials suggests correlation to be in the region of 1000 – 1500 hours depending on geographical location and local climatic conditions.

Please be aware that correlation statements in marketing literature should be used with extreme caution and that AWL Ltd would NEVER underwrite such a statement. If you do decide to take this route, please ensure you include a robust disclaimer!!

 It is our view that colourfast / photo-stability performance statements should be based on the test cycle, the exposure period and acceptance criteria usually based on dE shift and / or ISO 105 grey scale assessments.

 For example, Product X – Weathering performance standard is: BS EN ISO 4892-2 : 2012 – Cycle 1 – Method A – 1000 hours – dE shift <2 / ISO 105 A02 = 4 max. These are preferred ‘Performance Standard Statements’ recommended by AWL Ltd and similar is required from the BBA.

 AWL can provide a full explanation / interpretation of the above statement if required.

We can quote you for a 1000 hour test, but we cannot make any statements within the test report regarding +2 years of guaranteed photo-stability.

Sorry to be so negative, but I would not be doing my job properly if I do not make you aware of the complexities of accelerated weathering and the dangers of litigation using real time weathering correlation statements for products going into the marketplace during this contract review discussion.


Kind regards,

Paul Edwards.

Technical Director

Accelerated Weathering Laboratory Ltd



My response was a bit ‘War & Peace’ but hopefully it will educate those new to accelerated weathering in terms of its limitations and how best data can be used.

It is our view that any test house making correlation statements should only be doing so as a guide for costing advice and NEVER FOR warrantees or marketing literature statements.


Disclaimer: Although our email response was real, the recipient company name and personnel are fictitious to protect the innocent (just to show that although I can turn into a geek I still have a sense of humour which is important in this business). Any similarity to a company called Fudgit and Bodge Mouldings UK Ltd is by unfortunate coincidence only. No plastic mouldings or marketing people were harmed during the publication of this newsletter. Smile PJE.


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