CBA1??? Compare washing powders. Get old pillow case, cut into equal squares, soak in coffee (or similar).
Then, soak the squares for sane length of time in solutions of different washing powders! Lovely variables, easily controlled, etc.
for my cba i did it were i record how long it takes a cut apple to brown when i soaked it in lemoon juice, vinegar and i left one plain. Havent gotten results back but it worked out well:kissing_smiling_eyes: