In doing the research for the finish testing we came across the
http://www.smithandcompany.org/ website that describes the CPES we used in the test. There are several interesting articles on what it takes to protect wood from the elements. Regarding the difference between pigmented and clear products protection, the pigmented product designed for exterior use blocks UV and the clear products work by absorbing UV. After a time, the clear has absorbed all it can and it begins to break down. The pigmented (black) product continues to protect as long as the coating film is intact. It appears that clear can provide good protection until its absorbers quit working, then it needs to be sanded and recoated. Note that not all pigmented products provide UV protection.
Mar-Ktech
