This method is somewhat precise in making base dye mixtures and letting suprises occur once 

  the dye actually hits the fabric.

   Method is as follows:

1. For each dye, mix 2 teaspoons of powdered dye, 1 tablespoon of salt, and one cup of warm water in a tumbler. This forms a very concentrated liquid dye solution. Some colors (such as yellow) may need double or triple the amount of powdered dye to make the solutions "equally" concentrated, however, I usually don't worry about this.
2. Wet 1/2 yd. of fabric and put in a one gallon plastic baggie. Then do one of the following:
   • Mix one or more colors of dye concentrate with about 1/2 c. of water and pour into the baggie with the fabric.
   • Pour one or more colors of dye concentrate directly onto the fabric.
   • Pour 1/2 c. water into the baggie and then pour on one or more colors of dye concentrate.
3. Zip the baggie closed (with as little air as possible inside) and either let sit or smoosh the fabric around inside to move the dye through the fibers. Let the fabric sit or pick it up and smoosh it occasionally.
4. Mix a solution of 2 tablespoons of soda ash to 1 quart of warm water.
5. After 5-20 minutes, add 1/2 cup or so of the soda ash solution to the plastic baggie. Close the bag and smoosh everything around. At this point there is a chemical reaction taking place on your fabric. The soda ash reacts with the dye and bonds to the fibers. This reaction is mostly spent after one hour. Though some people feel waiting longer produces better results, I usually see little difference.
6. After an hour, dump the contents of the bag into a sink and rinse the fabric until the water runs clear. Do a final wash using Synthrapol. Ann Johnson recommends only draining the fabric in the sink and putting it directly into the washing machine. She agitates the fabric for only 2-4 minutes, then drains the water and spins it out. She does this a couple of times then does a full wash using Synthrapol.
7. Dry fabric in the dryer until damp dry and iron.

Some people soak the fabric in the soda ash mixture first and then add the dye as an alternative to steps 2-5. I  work the dye into the fibers of the fabric first because as soon as dye and soda ash touch, that chemical reaction starts taking place. I get a little more even color in the way I've described.

Have fun!