Soda ash fixer solution is one of the most important ingredients in making tie-dyed garments. The soda ash is used to alter the pH of your dye and fibres so the dye properly and permanently sticks to the fabric. If you're having trouble locating soda ash or simply don't wish to use it, you can use baking soda to alter the pH of your dye and fibres instead. When using baking soda you'll have to use extremely hot water to ensure the baking soda dissolves.
Fill a large saucepan with 4.5 litres (1 gallon) of tap water, and place it on your hob. Bring the water to boil.
Reduce the heat on the hob to keep the water at a simmer.
Pour the baking soda into the boiling water and stir with a spoon.
Add the garment, shirt or fabric that you wish to dye into the simmering water. Stir your garment in the water with a spoon for 10 minutes to ensure the baking soda dissolves into the fabric.
Take out your fabric and dye it as normal.
If using an all-purpose fabric dye, you don't need to use either baking soda or soda ash as a fixative.