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SPF testing
Is it possible to use sun sensitive paper to give a first hint of the SPF factor or is it a waste of time?
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5 Replies
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I’ve never heard of doing this but it might be a good predictor.
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The first question would be if the paper is reactive to visible light at all or just UV radiation? And then to determine which part of the UV spectrum it reacts to, A, B, or C?
Sunscreens are designed to block UV A&B radiation because that’s what causes damage. Most sunscreens try very hard to be transparent to visible light, and UV-C is harmless, if I remember correctly.If you have something UV-reactive, but not visible-light reactive, and you can put an even film of sunscreen over it, and you can use a reproducible/constant source of UV, I think it would probably be a good first-pass filter of sunscreen products - certainly enough to write a paper on, at least. Determining whether or not it’s predictive of actual SPF results would take lots of work. -
thanks Bobzchemist for a professional answer - i think it is hard to get the info on the exact wavelengths those papers absorb - however it may still be a cheaper alternative to a spectrophotometer.
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Oh, definitely cheaper than a spectrophotometer.
The website says that the paper is UV-reactive:It wouldn’t take much to run a very rough preliminary test, either. Maybe $100 in materials?applicator kit: http://gardco.com/pages/application/dp/sample_ease_system.cfm 3 or 4 commercial sunscreensPaperQuickly draw down all samples. Expose all papers to the sun at the same time. Evaluate results. -
Interesting that it is blue! I have a blue dye here that I bought for shampoo colour. On exposure to light - even a good desk lamp will do it - it turns turquoise. Maybe I can make some sun-sensitive paper with it!
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