I looked into how i could find out how permanent, permanent markers are.
I think i could experiment this by putting the same type of permanent marker on the same sized pieces of cardboard and put them into different solvents like water and detergent.
i would keep the experiment controlled by having the same amount of each solvent, same sized cards, same marker and same length mark.
I would test how fast the reaction is for each test and the independent variable would be the solvent i use. the dependent variable would be the length of time it takes each test to react to the solvent.