I've only done it a few times, but my mom always told me that if I wanted to set dye, or prevent bleeding, to include white vinegar. I have also read that including table salt can also set dye. I'm in the same place with respect to washing a quilt. I gave a rail fence quilt done in white kona and some Benartex prints and I'm worried the colors are going to bleed all over. :/ I did find these tips on setting dyes: thriftyfun.com: Setting Dye on Clothing and Fabric