If it were me, I'd soak it in a tub of vinegar, water, and mild laundry detergent. Why? Because my LQS owner gave me the Amish "recipe" for homemade "color catcher" solution . It's those three ingredients. I'm not sure what proportions for such a large quilt, but supposedly the vinegar that sets color. I don't understand the science, but the solution works when I don't have storebought Color Catchers.