Country or region: Washington, USA

Message: What is the difference between soda ash and washing soda? This is for pre-soaking before dyeing. Thank you.

There's an explanation on my page, "What is soda ash, and what's it for in dyeing?", in the FAQ section of my website.

Washing soda and soda ash are both sodium carbonate. Both will work fine as a high-pH presoak for tie-dyeing, to activate the fiber molecules so that they attack the dye molecule, forming a strong chemical bond. This works only for Procion MX or other fiber reactive dyes, such as Drimarene K or Remazol dyes.

Soda ash is the 99% or 100% sodium carbonate that is sold at the hardware store to use for increasing the pH of your swimming pool; look for a product with a name like "pH Up" or "pH Increaser", then check the fine print on the label to ascertain that it really is sodium carbonate.

Washing soda contains a lot more water than soda ash does, although it too is a dry white powder. At one time it also contained additives such as salt, perfumes, and whiteners, which must be avoided when you are dyeing. However, Arm & Hammer brand washing soda now contains nothing but washing soda, so it's fine for use in dyeing. You can often find it in the grocery store with other laundry additives. It's also a main ingredient in most laundry powders, though of course you cannot use those for presoaking your fabric for tie-dyeing.

The general rule with washing soda is to use three times as much as you would of pure soda ash, since the extra water molecules in the washing soda powder make it both heavier and bulkier, but this is not very important, because, as a somewhat weak base, sodium carbonate will produce an appropriate pH even if you use half as much sodium carbonate as the recipe recommends, or twice as much.

Note that neither soda ash nor washing soda will work to fix other classes of dyes. There is no point to using soda ash or washing soda with all-purpose dye, such as Rit or Tintex dye, for example, because it does not do anything to fix the dye to the fabric. Instead, if you use all-purpose dye, it is important to buy a cationic dye fixative, such as Retayne, and use it as an after-treatment to improve washfastness.

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