To set garment dye with vinegar, soak the clothing item in a large container in water mixed with 1/4 cup of salt and 1 cup vinegar per gallon of water. Stir the mixture and soak the clothing for 24 hours. Rinse the item with clean water, and if no dye is released during rinsing, hang it to dry. Once the item is dry, the dye is set. Wear and launder according to what is appropriate for the garment.
If the clothing item releases dye into the rinse-water, repeat the process once and rinse again. During the salt-and-vinegar bath, some dye may bleed into the water covering the clothing, but it will not negatively affect the dye setting. Wash the garment with like colors even after the salt-and-vinegar bath; this process will reduce bleed but may not entirely eliminate the possibility. If dye bleeds in the wash and stains other garments, treating the affected garments with diluted bleach or a commercial color-removing product may reverse the bleed.
For DIY projects, setting dye with heat is an additional option. Ironing the dyed fabric or heating it with a hair dryer (depending on the delicacy of the fabric) can aid colorfastness when applied to freshly dyed fabrics.