Acid inks require pretreated fabric for fixation and are printed directly to the textile then steamed to set the ink. The dyes that make up acid ink create ionic or electrostatic bonds with textiles such as silk, wool, and nylon. Fabric with reactive and acid ink must be washed after transfer to remove any residue. Reactive and acid-based inks also have to be set into the fabrics with a post-processing heating procedure to permanently set the dyes.