Name: Holly
Message: What's the problem with baking soda instead of soda-ash? I've tried baking soda on cotton materials, and it worked just fine. Is soda-ash better for other materials, could you please explain the difference to me?

What kind of dye are you using? I will assume a fiber reactive dye such as Procion MX dye, since that is the most popular dye for artists and craftspersons. This sort of dye works best at a pH between 10 and 11. (See What is the effect of pH in dyeing?.) All-purpose dye performs poorly on cotton at any pH.

Sodium bicarbonate, or baking soda, does not produce as high a pH as does sodium carbonate, or soda ash. Bicarbonate generally produces a ph around 8, while carbonate can raise it to 11.

A neat thing about bicarbonate is that it turns to carbonate in the presence of heat, so if you are baking or steaming your dye reactions, the pH will get to the ideal pH. In that case, baking soda is just as good as soda ash - better, in fact, if you wish to delay the dye reaction until you are applying the heat.

If you are not baking, however, and are using bicarbonate with fiber reactive dyes, you will have to use more dye, because so much of the dye you use will be wasted at the low pH; alternatively, your dye will not be nearly as well attached to the fiber, and will be much less washfast as a result. It really does work best to use the correct pH.