Any time I am washing fabric or a quilt I add half a cup of white vinegar to the load. White vinegar will set the dyes that aren't set and keep and color that wants to run from depositing on any of the other items in the washer. This trick I learned from a fabric historian at the Smithsonian Museum. It will also stop the deterioration of an old quilt top. The reason the old fabrics come apart is the fabric was dyed with acid dyes and the acid slowly eats away at the fibers. Fill the bath tub with cold water add a cup of white vinegar and then add the old quilt. Let it sit for an hour then let the tub drain. Then slip off your shoes and start at the back of the tub and walk the excess water out of the old quilt toward the drain. Then spread it out on a shady spot in the grass and let it dry face down. This will stop the acid dyes from eating away the fabric because it neutralizes it.