How do you clean a vintage burlap feed sack?

These vintage sacks are all 50 to 60 years old--so be careful how you treat them. Flour and feed sacks were made for the dye to stay in, to make dresses and aprons, and they can be washed with fabric detergent. Seed sacks , on the other hand, can not be washed or dry cleaned as the color will come out. It was made to come out in one washing, so the sack was nice and white and could be used to make dish towels and underwear. A dirty seed sack is of more value then a faded sack. I have over 300 vintage seed sacks of many colors and would never wash them. They are for display only.