Why Dye?
The precise orange of Velma's sweater doesn't exist in a commercial knit. The exact red of Jessica Rabbit's dress isn't available in heavy stretch velvet. Many character-accurate colours require custom dyeing rather than sourcing. Understanding fabric dyeing is a significant upgrade to a cosplayer's capability set.
Choosing the Right Dye
Dye choice is determined by fabric fibre content. Rit All-Purpose works on natural fibres and some synthetics. Rit DyeMore is specifically formulated for synthetic fibres. iDye Poly for polyester. Procion MX for the most colour-accurate results on natural fibres (requires soda ash fixative). Read the fibre content label on your fabric — dye formulated for a different fibre than your fabric will either not take or produce an unpredictable result.
The Discharge Method
For fabrics that are the wrong colour: discharge dyeing removes colour from fabric before applying new colour. This allows recolouring from a neutral base. Discharge agents include sodium hydrosulfite (strongest) and oxygen bleach (gentler). Test on a fabric sample first — not all fabrics discharge cleanly, and some produce unexpected undertones.