You can also take the piece, add a tiny bit of dish soap, run it under hot water, then cold water. You need to rub the wool while your doing this. It's the combination of the hot water, cold water, and agitation that will cause the fibers to felt. Some felters use only hot water but I think you'll get better results with the hot/cold. If you feel the fibers getting tight/dense - you've got wool.
