Name: Lucy 

Country: Canada

Message: Forgive me if this sounds simple, I am just learning this. Does the soda ash need to soak into the material once, or every time you do a full immersion dye, as done in Batik. Also if I use urea, do I need to use salt too?

What kind of dye are you using? Soda ash or another high-pH chemical is essential when dyeing with fiber reactive dyes, such as Procion MX dyes, but it's useless for direct dyes or all-purpose dyes, and actively harmful for acid dyes. Urea is handy for fiber reactive dyes, though not essential, but it, too, is no use for all-purpose dyes. In this answer, I will assume that you are using Procion MX dyes, since they're the best and most popular cotton dye among hand-dyers, and your questions don't seem applicable to wool. My answers would be completely different for a different class of dye.

Soda ash washes out easily, so every time you wash or rinse your fabric, you'll have to add it to your fabric again. Every new high-water-ratio immersion dye bath will need its own dose of soda ash added, too. 

Urea and salt have nothing to do with each other. Neither can substitute for the other in dyeing. 

Salt helps the dye to find the fabric if there's a lot of water. If you are using a large amount of water, as in tub dyeing or washing machine dyeing, you must add a lot of salt. If you are using a small amount of water, as in tie-dyeing or dye painting, you do not need to use salt. Salt is optional in low water immersion dyeing; it can increase the contrast in the patterns that form, but you don't need it for the dyes to work, since so little water is used in low water immersion dyeing.

If you are tie dyeing or dye painting, then urea is a good idea. Add it to your dye mixtures so that the dyes will stay wet on the fabric long enough for the dye-fiber reaction to occur. You can wrap your wet dyed items in plastic, instead, if you prefer, before putting them in a warm place overnight to react. However, if you are immersion dyeing, there's no need at all for urea, since there's already enough water present to keep the fabric from drying out before the dye reaction has completed. In some cases it might help in dissolving a little more dye, but in most cases you're better off using better dye dissolving techniques, instead of worrying about urea.

For more information, explore the Frequently Asked Questions section of my website; in particular, check out the section on dye auxiliary chemicals, such as the following:

• "What is soda ash, and what's it for in dyeing?"

• "What is urea for? Is it necessary?"

• "Do I need to use salt, in dyeing?"

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