Every quilter has his/her own fabric washing practices. Some never prewash, they just buy it, cut it, sew it, and when the quilt is finished they toss it in the sewing machine and hope for the best in terms of shrinkage and dye discharge. Other quilters prewash, and some even starch, every piece of fabric before they use it.
My habits lean more toward not prewashing but for block swaps it is usually recommended. I'm participating in Barb's churn dash swap so I wanted to prewash those fabrics and also threw in some fabrics from a kit I bought in December. I always use one or two colour catcher sheets in a prewash.
Just look at the dye it picked up! The sheets come out of the box white like the one on the left, and the pink sheets on the right show how much fabric dye was absorbed from the wash water. If the dye wasn't absorbed by the colour catcher, it would have likely run onto to other light coloured fabrics, turning everything a nice shade of pink.
But what really shocked me was that the fabric was a total mess and reminded me of why I dislike prewashing. It was a big wad of tangled, knotted threads and I had to use scissors to cut the threads to separate the fabric. Just look at the threads still tangled around the colour catcher sheet. It was like that with all the fabric. Then I read a brilliant tip from Carole about how to wash fabric yardage and gave it a try. It worked perfectly! Thanks Carole!
Summary of fabric washing tips:
Tip #1 - use a colour catcher sheet.
Tip #2 - accordion pleat the fabric and pin the selvage edges together.
Please pass along any additional fabric washing tips in the comment section.