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Pour salt and/or vinegar into the pot. Add enough cold water that you will be able to submerge your fabric later.  For berry dye, use 1/2 cup of salt for every eight cups of water. For plant dyes, use one part vinegar to every four parts water. Bring the solution to a boil over high heat. Reduce the temperature to medium-low to maintain a simmer. Submerge the fabric and allow the solution to simmer for one hour. You can use tongs to carefully lower the fabric into the simmering solution. Remove the pot from heat and allow it to cool. Remove the fabric from the pot and wring out the liquid. Hand wash the fabric with just cold water. If you’re in a hurry, you can drain the pot and cool down the fabric right away with cold water in the sink.

Summary:
Fill a large pot with a fixative solution. Add fabric to simmering solution. Rinse out the fabric.