Rit dyes are not made for protien substrates, acid dyes are. You have to watch your temps. Around 140 degrees F should do it. Washing feathers with any detergent will help if the feathers are dirty. Any liquid detergent in the dye bath is necessary. A couple drops in the quantity you are using. I would be concerned that in such a small amount of dye bath on a hot plate you risk burning the feathers.