How do you use citric acid as an auxiliary chemical for dyeing?

Citric acid is popular for use when dyeing with acid dyes, although it's not mentioned in most books on hand dyeing. Since it comes in powder form, it is more economical to ship than acetic acid (the acid that's found in vinegar), and it's much safer to work with (or to spill) than concentrated acetic acid. It is not volatile like acetic acid, so it won't fill your house with vinegar fumes when heated.

How much to use: follow a recipe or check your pH

citric acid in dye paint made with Procion MX dye for silk

Elin Noble, in her book Dyes & Paints: A Hands-On Guide to Coloring Fabric, advises the use of citric acid for curing Procion MX dyes on silk; it will not work on cotton or other cellulose fibers. Her recipe for dye paint calls for one teaspoon (5.8 grams) of citric acid crystals for each cup (or 250 ml) of dye stock solution. (For more information on using fiber reactive dyes under acid conditions, see Fiber Reactive Dyes for Protein Fibers.)

Citric acid as a substitute for vinegar and acetic acid

Kate Broughton's Textile Dyeing: The Step-by-Step Guide and Showcase advises the use of an equal volume of citric acid in acid dyeing recipes as a substitute for concentrated 56% acetic acid. Since ordinary vinegar in the US contains 5% acetic acid, as compared to the 56% acetic acid in concentrated acetic acid, you should divide the volume of vinegar called for by a factor of eleven, in order to find how much citric acid to substitute for it.

ProChem's recipe for Rainbow Dyeing using WashFast Acid Dyes indicates that six tablespoons, or 105 grams, of citric acid is equivalent to six tablespoons, or 54 grams, of ammonium sulfate, or one liter of white vinegar.

Another recipe by ProChem indicates that 2 tablespoons (35 gm) of dry citric acid crystals equals 2 tablespoons (56 gm) of sodium bisulfate, which equals 22 tablespoons (330 ml) of white distilled vinegar. This is the amount they recommend for adding to 2.5 gallons of water, to dye one pound of wool, using Procion MX dyes. They recommend more acid for using Procion Mx dyes as acid dyes than they do for the other acid dyes they sell.

Check your pH

If you have pH paper, you can easily determine how much citric acid is needed to reach a specific pH in your dyebath, before you add the dye.

pH needed for different acid dyes

dye class	pH range
Leveling acid / Kiton / Strong acid	2.5 to 3.5
Milling acid / Weak acid	5.2 to 6.2
Super Milling / Fast Acid	5.5 to 7.0
Lanaset	4.5 or 5.0
Procion MX used as acid dyes	2.5 to 3.5

Safety

Although citric acid is a safe ingredient in foods, it's important to note that pure citric acid powder and strong citric acid solutions are much more irritating than diluted citric acid, to the skin, eyes and respiratory tract, enough to cause harm if you are careless. Treat it with the same respect that you do any chemical powder: wear gloves to avoid excessive skin contact, and wear safety glasses or a face mask if necessary. Don't breathe citric acid dust, and don't risk getting strong solutions of citric acid in your eyes.

Citric acid is not as safe to work with as ordinary vinegar, but it is much more safe than concentrated 56% acetic acid, and safer still than glacial (99.5%) acetic acid, which makes it more convenient to use.

Where can you buy citric acid?

Many dye suppliers sell citric acid; when you're ordering dyes anyway, it's convenient to buy your citric acid from your dye supplier.

To find citric acid locally, look for a store that sells supplies for home beer and wine making, or a specialty Indian grocer. It's sometimes also available under the name "sour salt". Some baking suppliers sell it for use in making bread dough extra sour. Suppliers of materials for making bath salts and bath bombs tend to have good prices.

Citric acid is not vitamin C

Confusing citric acid with ascorbic acid (vitamin C) is a common error, because everyone knows that citrus fruits are a good source of both citric acid and vitamin C. Don't confuse them when shopping for dyeing supplies. They are completely different chemicals. Ascorbic acid is much more expensive than citric acid, and it's not as good, because it's commonly diluted with inert chemicals. See the March 13, 2010 entry in my hand dyeing Q&A blog, "Can I use ascorbic acid in place of citric acid when dyeing with an Acid dye?".