There are varied opinions among experienced quiltmakers about whether all fabrics should be washed before using. Some quilters wash, dry and iron fabrics as soon as they get them home. Others choose not to wash the fabrics at all. Which way is best?
There are two reasons to wash the fabric before using. The first is that it might shrink. Good-quality fabrics are preshrunk and shrink much when washed.
The second reason is to determine if the fabric is colorfast. Prewashing fabric will not guarantee that the dye in the fabric will not run the next time it is washed. Using the home remedy of vinegar or salt-water rinses will only prevent the fabric from running in that wash, not subsequent washes.
Rinsing fabric until the water runs clear only continues to pull dye from the fabric, dulling it. It does not guarantee that the fabric will not run again in the future.
Harsh detergents will draw more dye so try to use a mild soap made especially for quilts and old fabrics. Ask about these products at your local quilt shop.
Quilters who piece by machine don't like to prewash their fabrics. The stiffness in the fabric is considered a plus for machine piecing, and the little bit of shrinkage that occurs after the finished quilt is washed helps to hide the actual machine-quilting stitches.
If you decide not to prewash your fabric, test the colorfastness of the darkest fabric in your quilt against the lightest fabric in your quilt. Wash a small piece of both fabrics using the soap with which you intend to launder the quilt. Let one fabric piece dry on top of the other. If the darkest fabric doesn't run onto the lightest fabric, you can be confident about using them without prewashing. If it does run, you may want to reconsider use of the fabric.