when i was doing more needlework & cross stitch than i do now, the lady @ the needlework shop told me to soak the overdyed floss in cool water with white vinegar to "set" the color. i have done that on all my dark colors since i started quilting then washed & dried on the hottest settings i have on my machines, which is "sanitize" several fabrics have shrunk a little, but nothing has run...now i buy white vinegar by the gallon @ bjs!