Step 4Soaking the shirt
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To enable the Procion dyes to bond with the shirt, you need to soak it in a solution of WARM water and soda ash for about 10 minutes. Follow the instructions given with the soda ash so that you have the right mix. Do not use water that is too hot or too cold - and add a couple of table spoonfuls of common salt to the mix too!! Make sure the mixture is thorougly dissolved before adding the shirt. The temperature of the water should be about about the same as a baby's bath! As the soda ash is slightly caustic you may want to wear rubber gloves at this point, especially if you have a cut on your finger - it will sting! After soaking, wring the shirt out thoroughly. The more liquid that you can squeeze out, the more dye will be able to get in! I usually spin my shirts on the spin cycle of the washing machine. (note if you use a brand new shirt, wash it first to remove the newness, which I think they call "size", This "sizing" will prevent dye from bonding properly, and you may get a streaky effect.)
Soda Ash isn't the same as baking soda. you can buy it from a dye store or get it at a pool and spa store. It is caustic so be sure to protect your hands and eyes.
As for banding. Once you twist your shirt into a bun. (I use a fork and twirl like its pasta) Just take your rubber band, hold it open and slide it under , and around the shirt while it's sitting flat. Do that 2 more times and you'll have your triangles. (almost looks like a pie chart at this point.)
Once you've allowed the garment to sit dyed for 24 hours, rinse, then wash with the hottest water for the garment in the machine...with Syntrapol or similar product. The shirt is amazingly color fast. I have one dress I bought about 5 years ago that the colors are still vibrant... the fabric is showing wear... but the colors are still awesome.