What can I use for a tie dye shirt if I don have soda ash?
Tie dyeing is a technique. It requires different supplies for different fabrics. Tie dyeing silk is much different than say cotton. Soda ash is used as a presoak to raise the pH level of the garment so that the fiber reactive dyes can work at room temperate. When using silk to tie dye soda ash is to harsh, a vinegar solution is used instead. The process also will differ with different dyes.
Alternately you can use baking soda as the dye fixer. But, baking soda produces a more washed out tie dye. It also requires a higher temperature to set the dye than soda ash.
If you are new to tie dyeing and have little knowledge about dyes and the dyeing process I suggest you start with a simple method like using Rit Dyes. They require no dye fixer unless you are using silk or wool. It’s much more user friendly for beginning tie dyeing. I would also suggest looking up Dharma Trading Company, they have a lot of useful information on dyeing.
Traditional tie-dyeing methods involve using soda ash to help adhere the fabric dye onto the fibers. However, most people do not have access to soda ash. One solution is to use salt instead of soda ash to encourage the dye to bond to the fibers. When you use salt instead of soda, the dye bath solution is safe for the skin, making it appropriate for younger children to work around.
Source — http://www.ehow.com/how_8128588_tiedye-soda-ash.html