Hand-dyeing in your washing machine is an easy way to change the colour of fabric. The washing machine does most of the work and drains away the mess. To keep the new colour, make the hand-dyed fabric colour-fast by adding a fixative to the dye bath.
Weigh the dry fabric for reference.
Prewash the fabric with Synthrapol or Orvis detergent. Unlike commercial laundry detergents, these do not contain any additives that may interfere with dyeing.
Fill the washing machine with enough warm water to cover the fabric comfortably.
Stop the washer and add the dye to the water. For deep shades, add 28.4gr. of dye per pound of fabric. Let the washer agitate a little to dissolve and distribute the dye.
Stop the washer again and add the fabric to the washing machine. Let it agitate for about 10 minutes. You may have to reset the washing machine to allow this to happen. Don't let the water drain out of the washer.
Stop the washer to add salt. The salt helps the dye migrate onto the fabric; it does not set the dye. For a pound of fabric, add 2 to 4 cups of salt. The more salt you add, the deeper the colour.
Let the washer agitate for about five minutes.
Put on rubber gloves and face mask.
Stop the washer and add the soda ash. This chemical sets the dye onto the fabric. For a pound of fabric, add 70.9gr. of soda ash. Do not add it all at once, but in two or three small batches, agitating the washer in between batches to dissolve and distribute the fixative evenly.
Let the washing machine complete a cycle that is at least 15 minutes. Let the cycle complete so the dye bath drains out of the washing machine, followed by a rinse cycle.
Leave the fabric in the washing machine, and wash it again with Synthapol or Orvis detergent. Use whatever water temperature you would normally use for this fabric.
This procedure is not recommended for a front-loading washing machine because you cannot manually stop and start these machines. This procedure will not work for wool or other protein fibres. You need a different type of dye and fixative.
Use care when handling soda ash as it is caustic. Wear gloves and a mask.