I just purchased some beautiful blue batik. I asked at the lqs if I needed to prewash and was told no. I had been told to test the fabric by using a wet paper towel or white cloth and rub on fabric. If no color comes off it is ok. I did this with the blue fabric and some color came off so I decided to put it in the sink with some warm water. The color just ran out of it. It is still beautiful but not nearly the same shade as when I bot it. I can still use it but not for the quilt I bot it for. Thank goodness it was only going to be the binding. I then washed it in the machine with Retayne and it seems to be ok now.