Follow these steps to remove mustard stains from leather or suede:
- Although mustard usually causes permanent stains on these materials, try mixing a solution of mild soap in lukewarm water, swishing to create a great volume of suds, and applying only the foam with a sponge.
- Wipe with a clean cloth dampened with clear water.
- Dry with a soft cloth.
- On leather only, follow with cleaners such as Tannery Vintage Leather Cleaner & Conditioner or Fiebing's Saddle Soap to condition the leather.