I dont prewash and when I do wash ,I use cold water and gentle detergent.

I will pre-wash fabrics if they are bright bold reds, purples, royal blues, etc. I will wash they with Retayne to set the colors. The rest of the quilt fabrics I will wash separately and throw in a color catcher. If I don't have any bold fabrics to set the colors then I don't pre-wash. So....I will either wash all the fabrics of a quilt I am going to make to make sure of uniform shrinkage, or I won't wash any of the quilt's fabrics. It all depends on the fabrics being used in the quilt. Does that make sense? Clear as mud? I always wash in cold water and set dryer to normal heat. I have found Retayne at my LQS and the color catchers are sold at WalMarts, Targets, and most supermarkets in the laundry soap aisles.

someone posted on here about possible "rat contamination" on fabrics coming from other countries. Don't know if it is true but it grossed me out enough to pledge to prewash

I don't and have never had problems

Always batiks.

To wash...or not to wash...that is the question? I wash all fabric from an unknown source(yard sale, thrift shop etc.) I test fabrics from LQS if I suspect it might be a bleeder. Wet a square of the suspect fabric in the sink in hot water, scrunch it just a little and sit it on a white paper towel to dry. If any colour is on the paper towel, I wash the fabric in Retayne and then proceed to dry and iron it to use.
After a quilt is completed, the first time I wash it, I throw in a couple of Color Catcher sheets and have not had any problems. Color Catcher sheets are made by Shout and can be found in the laundry aisle at Target, Walmart etc. Some people like to also add Synthrapol that suspends any loose dye in the water (and not on the quilt) If you do encounter a problem, do not dry the quilt until problem is resolved. Retayne or Synthrapol are usually available at LQS?

I don't prewash. Never had any problems.

I don't pre-wash. I pay between $8-$10 a yard for fabric. With fabric of that quality, I shouldn't have to pre-wash, and I've never had problems, even with reds and purples.

Interesting timing. I don't prewash - ever. I've never had a problem. Tonight, I was getting ready for a class and it said you had to prewash and starch the fabric. I thought about skipping that, but didn't want a problem in the class so decided to wash. I found out one of the fabrics was a bleeder. I had to wash several times and then use vinegar to finally get the color set. Guess my guardian angel was looking over my shoulder.

I never pre-wash. :)