Originally Posted by Prism99

MacThayer, I think your test run confirms information on the web. However, I want to clarify that neither Synthrapol nor Dawn will set dyes. All they do is suspend unset dye particles in water so they are rinsed away instead of settling into fabric fibers.

Most fabric that "bleeds" has had dyes correctly set by the manufacturer but have not been rinsed sufficiently. Fibers can absorb only a limited amount of dye particles. Excess dye particles that are not rinsed away by the manufacturer end up in color catchers (such as those in your test run). Most of these excess dye particles come out in the first wash, and subsequent washes have color catchers that come out pretty clean.

When the manufacturer does not actually set the dye properly, the end result is a "bleeder" fabric that never stops bleeding. It's not just a problem of excess dye particles (more dye particles than the fibers can absorb) not being
rinsed away; it's a problem of all dye particles not being permanently set into the fibers. Synthrapol and Dawn will prevent these loose dye particles from settling into other fabrics, but they will not stop the fabric from bleeding in future washes.

Hope this explanation is clearer than mud!