Batiks do not ravel so washing pre-cuts of any type (jelly-rolls, charms, etc) is actually quite safe - safer than not washing them, imho. The key with prewashing batiks (and any fabric that runs) is to wash it until it stops running. In order to know when that point is reached, you have to retest for bleeding after what you believe is the last wash, i.e., the one where the Color Catchers remain white.