There are a few ways to do this. The best way I can think of is to start out the paint with no additives and have that as a control. You can test that on whatever your painting or do it in a lab with heat lamps and lights if that is a possible option. However you decide to do the testing, after starting with the control test, add different additives and see which ones fades less the original without any additives. This is the best scenario for a simple yet informative test.
Hope that helps!
