To remove a mustard stain from a silk garment, if the garment is washable silk, first rinse in cold water. Then gently rub a protein hair shampoo or a liquid enzyme detergent, such as Era, into the stain and allow it to sit for a few minutes. Soak 12 hours in soapy water. Rinse well. Don't twist or pull. Handle the silk gently and hang it to dry. If the silk is not washable, have the garment dry cleaned.