I just made a table runnner using pre-washed batiks (I washed them 3 times). Well, when I steamed the seams the dark still bled onto the light right on the seams (if I had used Harriet Hargrave's test to wet, put it between paper towels and put a weight on it I would have known to continue washing). I will be throwing the top in the wash with come color catchers and see if I can get the color out. I don't normally prewash everything because I do test, but I may just bite the bullet and do all of it.