One of the steps in tie-dying is to soak the shirt in a “fixer” solution of sodium carbonate, also known as soda ash. I think of soda ash as a dye-cotton binding agent.
My informal experiment is to see the effects of applying the soda ash before or after folding or not at all. Here are the results of four spirals:
Soda Ash – Tie – Dye
The first brown-red spiral is my usual technique of soaking in soda ash solution before folding. It gets good dye coverage, but looks a little blocky in places. On reason I like this order is that soaking after tying sometimes loosens the folds/knots.
Dampen – Tie – Soda Ash – Dye
This is the Paula Burch technique, since it is safer not to handle the treated fabric. The effect is more pronounced since both the soda ash and the dye are constrained by the tying; however, there is less dye coverage.
Dampen – Tie – Dye
Skipping the soda ash produced a nice pattern, but the colors (brown and periwinkle) already look faded and I suspect they will fade quickly over time. On the other hand, you can view the colors as nicely mellowed.
Tie – Dye
Dry cloth produced bulky folds and really soaked up the dye. The green did not “mellow” well for whatever reason, possibly unrelated to the technique.