To wash...or not to wash...that is the question? I wash all fabric from an unknown source(yard sale, thrift shop etc.) I test fabrics from LQS if I suspect it might be a bleeder. Wet a square of the suspect fabric in the sink in hot water, scrunch it just a little and sit it on a white paper towel to dry. If any colour is on the paper towel, I wash the fabric in Retayne and then proceed to dry and iron it to use.
After a quilt is completed, the first time I wash it, I throw in a couple of Color Catcher sheets and have not had any problems. Color Catcher sheets are made by Shout and can be found in the laundry aisle at Target, Walmart etc. Some people like to also add Synthrapol that suspends any loose dye in the water (and not on the quilt) If you do encounter a problem, do not dry the quilt until problem is resolved. Retayne or Synthrapol are usually available at LQS?