Before you begin a quilting project, it's important to first wash quilt fabrics. This will remove some of the chemicals added by the manufacturer and make it easier to quilt. Also, cotton fabric does shrink, and most of the shrinkage will occur during the first washing and drying. Be sure to use settings that are as hot as those you intend to use with the finished quilt.
Dark, intense colors, especially reds, tend to bleed or run. Wash these fabrics by themselves. If the water becomes colored, try soaking the fabric in a solution of three parts cold water to one part white wine vinegar. Rinse thoroughly. Wash again. If the fabric is still losing its color, discard the fabric and select another. It is not worth using a fabric that may ruin the other fabrics when the finished quilt is washed.