to prewash or not to prewash....
the bleeding thing can ruin a day. your quilt goes in the washer a red and white quilt, but comes out a pink and red quilt...i can offer help.
Synthrapol (i get mine from Dharma Trading). dyers use it to prepare fabric for dying and after to help pull out excess dye. (i have my suspicions that it is the same active chemical as in shout's color catchers..just saying)
the coolest thing for quilters about synthrapol is that it neutralizes the chemical bond a dye particle floating in the water has that would otherwise stain the lighter colored fabrics. (it can be used in prewashing fabric that will be used in fusible applique too.)
i love this stuff! i use 1/4 cup per queen quilt and wash as normal. i do add a little regular detergent to the water to make the quilt smell good. if you don't it'll smell like ironed batiks. the trick is to let your washer fill completely with water and agitate a couple times, then add your quilt. that way the synthrapol is fully mixed in the water. (for you front load owners- there is a low foam version available)
there is another soap called Retayne. I'm not a fan of it cause it has 'fussy' instructions. you have to add so much per yard..blah blah blah....wash the first time in hot water then after that in cold...blah blah blah. synthrapol- just add it to the water, wash, and not have to worry about it again.
want proof? i had a customer bring me a very vintage applique quilt that her mother had done backing in the 30s. it was a bouquet tied with a deep purple ribbon on an off white background. you guessed it- the purple had bleed very badly onto the background. i offered to wash the quilt with synthrapol, what could it hurt? not only did it remove the bleed, we discovered that background was white fabric, not off white.
i am not a paid endorser (i wish) for either synthrapol or Dharma Trading. i offer only my honest opinion based on personal previous experience (at least 10 years worth of washing quilts) do with it what you want :)