What is the purpose of using sodium sulfate, when dyeing fabrics with Procion MX dyes?

Name: Jennifer

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Sodium Sulfate
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Sodium Sulfate: Handbook of Deposits, Processing, & Use

by Donald E. Garrett

Message: What is the purpose of using sodium sulfate, when dyeing fabrics with Procion MX dyes? I have seen instructions both with and without using it. If I decide to use it, do different products cause different results?

This is really two questions: 1, what is the purpose of using salt when dyeing with Procion dyes, and 2, what is the difference between Glauber's salt (sodium sulfate) and regular salt (sodium chloride), when dyeing with Procion dyes.

The first question is covered in my FAQ page, "Do I need to use salt, in dyeing?" . Whether you need to use any salt at all, including sodium chloride or sodium sulfate, depends on what kind of dyeing you are doing. You do not need to add any salt when you are tie-dyeing or dye-painting, because the dyes being used are so concentrated. You do need to add salt to your dyebath for high water ratio immersion dyeing, as when dyeing in a washing machine or a five-gallon bucket, to prevent dye from being wasted in the large volume of water; using a large amount of salt helps keep the negative charges of the dyes and the fiber from causing them to repel each other. Using salt in your high-volume dyebaths helps to increase the color yield you get from a given amount of dye.

You don't need to add salt to dye concentrates used for tie-dyeing or dye painting because the total volume of water is so low, relative to the amount of dye and fiber, that the dye manages to find the fiber anyway. In addition, adding salt to dye concentrates can be a problem, because salt reduces the solubility of dye. If the dye in your mixture becomes insoluble, dropping to the bottom of the container in the form of powder, because the addition of too much salt has reduced its ability to dissolve in water, then your colors will end up very pale. I've had this happen to me, so I recommend against adding salt to your dye concentrates.

For low water immersion (LWI) dyeing, the amount of water used is small enough that your results will be good and intense even without salt. However, adding salt to your low-water dyebath will tend to increase the sharpness of the crystalline-like patterns that are formed in LWI. Don't add the salt directly to your dye concentrates; instead, add a strong solution of salt to your fabric. I like to add salt to my LWI baths along with the soda ash, after the dye has been soaking into the fabric for at least a few minutes.

The second question is, why use sodium sulfate, instead of sodium chloride? Sodium sulfate is more expensive, after all. Sodium sulfate and sodium chloride will do pretty much the same thing in a fiber reactive dyebath. Why not use the cheaper and easier-to-buy sodium chloride?

Although both are salts, and the two have a lot in common, sodium sulfate has some different properties than sodium chloride when used with acid dyes. Sodium sulfate slows the attachment of acid dye to fiber via the sulfate groups in the dye molecules, and thus aids in getting a more level, even color, but that's not an issue when working with fiber reactive dyes. Reactive dyes don't bond to fibers via their sulfate groups, the way acid dyes do.

The one reason I've seen for recommending sodium sulfate instead of sodium chloride, with reactive dyes, is that it is supposed to intensify the color of copper phthalocyanine based dyes, such as Procion Turquoise MX-G. For example, Dharma Trading Company says in their catalog,

"Improves the yield of Turquoise Fiber Reactive Dye. (Gives more intense color). Use in place of,and in the same proportions as, Plain Salt, when dyeing solid shades of #25 Turquoise or colors mixed with #25 (marked with T on the color chart)."

(There's more information on this particular dye on the page "A Beautiful Blue: Procion Turquoise MX-G".) I don't know why this particular dye structure is supposed to be more affected by sodium sulfate than other dye colors are. Having something improve the yield of one dye color more than other dye colors could wreak havoc with color mixing, if not enough testing is done first.

If you're dyeing something a pure turquoise, using Procion turquoise blue MX-G, for example, then, according to this recommendation, you might get a more intense turquoise color, for a given amount of dye, if you substitute sodium sulfate for sodium chloride, or perhaps you can get away with using a smaller amount of turquoise dye, for the same color intensity. As with sodium chloride, you wouldn't want to do this with tie-dyeing or dye painting, because of the solubility problem, but you could use it in solid-color dyeing, or in low water immersion dyeing.

If you are dyeing anything with a mixture of dye colors, however, including not only Procion MX turquoise MX-G but also at least one other color of dye, then using sodium sulfate could alter the balance of color, and therefore your hue. If you are using a pre-mixed color, or a color recipe you've perfected without the use of sodium sulfate, then sodium sulfate will make the final result more blue in color, if it's true that sodium sulfate acts this way. Substituting sodium sulfate for sodium chloride might change a green mixture to a bluish one. Note that of the hundred or so colors sold by the best dye retailers, such as Dharma or ProChem, only a dozen or so are pure single-hue dyes; the others are mixtures of two or more dye colors.

Substituting sodium sulfate for sodium chloride makes a great deal of sense to try if you're dyeing several tons of garments the exact same color, because the trial and error of getting the exact right hue, by varying the amount of each dye you use, would be well worth the effort in order to reduce the cost required in buying large quantities of dye.

If you're doing very small-scale hand dyeing, though, it makes much less sense to even try this. If you buy premixed colors of Procion MX dye, you expect your result to end up similar in hue to the color chip in the catalog of your supplier. If you have already worked out recipes to mix your own colors, using sodium chloride in your dyebaths, then your colors might change when you substitute sulfate for chloride. It might not be worth all the trial and error of figuring out exactly how much less turquoise dye powder you can get away with using, by substituting sodium sulfate for sodium chloride.

(I should point out that I have not experimented myself to see how big a difference in dye yield there is for turquoise as opposed to other colors of dye. Turquoise is noted for suffering more from a cold studio temperature than other colors do, since it reacts more slowly than they do; is it possible that this is the only reason why sodium sulfate is supposed to make a bigger difference in color yield for turquoise-based dyes than for other colors? Be sure to include notes on temperature when you do your own tests.)

I recommend using sodium sulfate as a substitute for sodium chloride with Procion MX dyes only when you are experimenting. It's always wise to do tests before any large or important project, anyway. Changing from one salt to another is fine if you do a good series of test swatches first to make sure what color you will get, and it's also fine if you're not testing at all but will be happy with the unexpected. If you have some sodium sulfate on hand anyway, and you're doing some low water immersion dyeing, go ahead and try sodium sulfate to see what happens. Don't do it if you're not willing to risk getting a different hue than you expect.

Interestingly, sodium sulfate is commonly used to dilute dye powders to a standard strength per gram. The same type of dye from one retailer may contain sodium sulfate, while that from another retailer may contain a synthetic tannin as a diluent powder, instead. (See my page, "What is in dye powder?".) Colorado Wholesale Dyes makes a point of selling dyes that don't have extra salts added to them as diluents; they think this makes it easier to wash out excess dye after dyeing, but it could also make a difference in the reproducibility of colors you mix yourself. The presence of salt certainly does make a difference in how much dye you can dissolve in a certain amount of water.

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Posted: Thursday - November 10, 2011 at 08:27 PM

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What is the purpose of using sodium sulfate, when dyeing fabrics with Procion MX dyes?

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