Do we need to use soda ash with Rit dye?
No, soda ash will not make all purpose dye, such as Rit® or Tintex®, permanent on the fabric. Instead, you must either use a washfast dye such as Procion MX dye, which does require soda ash, or use a commercial cationic fixative in order to make all-purpose dye acceptably washfast, so it does not bleed in the laundry forever.