the person who mentioned the Synthropol.....it is a product used in the wash to keep dye that may come out of fabric from getting on other fabrics in the wash- it does not stop the fabric from bleeding in the first place- just keeps the dye suspended in the water- protecting the fabrics around it- it is necessary to use it as the directions state (washing in HOT water- which many people do not really want to do) often used after a quilt is finished & you may be afraid one of the fabrics in the quilt might run & ruin surrounding fabrics- then the synthropol is put in the wash to help keep that from happening. if you are pre-washing yardage just wash- with regular detergent- check the rinse water- if there is dye in the water- rewash & rewash until there is no more bleeding. good quality *like the Michael Miller and Kona blacks don't tend to bleed- but there is always a chance with a deeply saturated color for some excess dye to come out in the wash so always a good idea to either pre=wash or at least test before cutting the fabric.