I wash a lot of my fabric and some I do not. For the precuts, if they are dark fabric, I put them in a bowl in the kitchen sink in very warm water and carefully swish them around checking for any color problems. Then squeeze out as much water as possible, lay a towel on the ironing board and press with a dry iron til just about dry. Hang on plastic hangers and they are ready to go. The washing and ironing seem to take care of any potential problems that might occur. I do this with jelly rolls, charms, and layer cakes.