Why can't you use the pot after dyeing?

If you use metals or acids in a dying process to extract brighter colors, these substances can leave a highly toxic residue that affects the integrity of the metal. The amount of salt and/or vinegar used for dying create chemical reactions that can change the toxicity level of something normally considered safe to ingest or cook with. A metal pot used for dying will degrade at a faster rate than one used solely for food, especially if it has a non-stick coating. Small particles could leach into your food and make you very, very sick, so it's better to be safe and dedicate one pot for dying and store it outside the kitchen so it's not used for cooking by mistake.