Country: USA

Message: Can I use ascorbic acid in place of citric acid when dyeing with an Acid dye?

That's an interesting question! I don't recommend doing so, but I am sure that it could work, if you use the right amount of ascorbic acid powder to achieve the same pH that you normally use for a particular dye.

I don't advise substituting ascorbic acid for citric acid, largely because of their relative cost: powdered ascorbic acid typically costs $14 to $20 a pound, while citric acid costs only about $4 a pound. Using a nutrient in place of citric acid seems wasteful, when all you want is the acidity. (It's easy to find sources for citric acid to buy, as mentioned in an earlier blog entry here; most dye suppliers sell citric acid inexpensively, as does Amazon, as well as home brewing suppliers.) Note also that crushed vitamin C pills are not at all the same thing as pure ascorbic acid powder, because other ingredients are added in the process of making pills, such as lactose or magnesium stearate.

(I've known several people who confused these two different chemicals. Thanks to the coincidence that citrus fruits contain both citric acid and ascorbic acid, many people think that citric acid is the same thing as vitamin C, when, as you probably already know, only ascorbic acid is vitamin C.)

Beginning dyers usually start by using distilled white vinegar as their acid, for dyeing with acid dyes. Distilled white vinegar, in the US, is 5% acetic acid, unless labeled otherwise, though it is possible to buy distilled vinegar at strengths up to 10%, usually sold for cleaning purposes. Advanced dyers may use the concentrated form, glacial acetic acid, which contains 56% acetic acid, because it takes a lot less space and may end up costing less, but glacial acetic acid can be quite dangerous to work with. (Always add acid to water, not water to acid; when possible use pipettes instead of pouring the acid; and wear goggles or a face shield, in addition to reliable waterproof gloves and protective clothing.) You can substitute one-eleventh as much glacial acetic acid in dye recipes that call for vinegar.

Citric acid makes an excellent substitute for vinegar or acetic acid, because it's safer to work with than glacial acetic acid, it's less expensive to ship since it's in powdered form, and it does not boil off, causing unpleasant odors in the workspace, as acetic acid does. PRO Chemical and Dye recommends substituting one teaspoon of citric acid powder for one teaspoon of glacial acetic acid, though it's better to consult a specific recipe, if possible, that tells you just how much citric acid to use with your particular dye.

If you want to substitute ascorbic acid for citric acid, how much should you use? As a general rule, try to produce the same pH in your dyebath as you have already been using. One way to do this is to make up an identical dyebath, with the exception of not including the dye, so that you can see the color of your pH paper. Test the pH when you make up your dyebath (without dye) according to your usual vinegar or citric acid recipe, and then duplicate the dyebath without the acid, this time adding the ascorbic acid until you reach that same pH. How much ascorbic acid is likely to be required? The pH of a 21 gram-per-liter solution solution of citric acid is 2.2.  Ascorbic acid, in contrast, produces a solution with a pH of 3 if you use 5 milligrams per liter, and it produces a pH of 2 if you use 50 grams per liter, so you might estimate that twice as much ascorbic acid is required, by weight. Since the density of ascorbic acid, 1.65 grams per milliliter, is not far from that of citric acid, at 1.54 grams per milliliter, you can estimate that you might use about twice as much ascorbic acid by volume, as well. Note that this is just an estimate, since both citric acid and ascorbic acid are what are known as weak acids; the performance of weak acids is a little bit complicated and very difficult to calculate, since they don't fully dissociate into ions when dissolved in the same way strong acids do.  It is best to test your recipe, making the dye-less dyebath to determine for certain how much ascorbic acid will give the same pH as your usual recipe that uses vinegar or citric acid.

It's important to adjust the pH of your dyebath to a suitable degree for the type of dye you are using. For a weak acid dye such as the WashFast Acid Dyes, the desired pH in the final dyebath is only mildly acidic or even neutral, between 5.0 and 7.5. In contrast, strong acid dyes such as the Kiton dyes, or as Procion dyes when they're used with acid instead of soda ash, the desired pH is considerably lower, typically between 2.5 and 3.5, so a larger amount of acid must be used when dyeing with these dyes. Using a lower pH than is optimal will tend to reduce the levelness of your dye color, resulting in more variation in color intensity between different parts of your fabric or yarn.

If you do decide to go ahead and use ascorbic acid in place of citric acid, please let me know how it works out.