SPF Sunscreen

So I've researched some things on the sunscreen vs sunscreen under make up. I decided to tweek the experiment a bit and do something similar to it. I want to test the difference of the SPFs in sunblocks and I also wanted to see if a more expensive sunblock was more effective than a cheaper one.

I found I could test this by using 4 different spf sunscreens, 4 different brand sunscreens, photo paper, clear plastic folders and a photographic fixer. My mother's friend is a photographer and he may be able to help me get the photographic fixer. (Hopefully lend it to me if he has one!) After cutting the photo paper in equal squares and label 1, 2, 3 and 4 to make note of which sunscreen is which. I will measure a certain amount of sunscreen and spread each type on 4 separate photo papers. Then I'll carefully place them into the clear plastic folders, then place them out on the driveway for five minutes. After the five minutes is up, I'll take the results to a dimly-lit room (so I don't affect the results). The papers will be carefully removed and, lay it glossy side down in the photographic fixer. The results, hopefully will indicate, which one sunblocks are more effective and price worthy. The sunblock which allowed the least least amount of sun penetration will turn white, and the most will turn dark.