I prewash all. Don't want any surprises after all that work. I have only so much time to piece for myself after LA work. I even prewashed Hoffman Bali pops. Good thing, too. Did it in the sink with Hot Water and Retayne. Learned a lesson there. Had to use bleach to get dye out of sink. Took 2 washes of Retayne and 2 rinses. Spun out water a few strips at a time in a salad spinner and hung on clothes rack to dry. Then pressed (not ironed). Now I am happily piecing worry free.