Name: Catherine

Message: I am trying to find out about the chemistry of the "Alter Ego" dyes which dye silk & rayon differently in the same dye bath (I got my kit through Dharma Trading).  I am using this as a part of a Science of the Arts course I am teaching to high school students & would love to know more about the chemistry...

Alter Ego® dyes are apparently a mixture of direct dyes with acid dyes, plus auxiliary chemicals, probably including a reserving agent and a cationic dye fixative. Unfortunately, they are not among the simplest or most understandable examples of dye chemistry that one could choose for a chemistry class.

Direct dyes are typically large molecules that remain associated with textile fibers via fairly weak bonds, a combination of the relatively weak Van der Waals forces and some hydrogen bonding. Acid dyes bond to protein fibers by the formation of salt linkages between sulfonic or carboxylic groups in the dye and the side chains of certain of the amino acids in the protein fibers. See "What kinds of chemical bonds attach dyes to fibers?". To complicate matters, some acid dyes can act as direct dyes, and all direct dyes will color silk.

The interesting thing about the Alter Ego dyes is the way they prevent the direct dye in the mixture from dyeing the silk. As a general rule, all direct dyes work on cellulose fibers, such as rayon, and also on silk, which is a protein fiber. There is something called a reserving agent, as far as I can tell some sort of syntan (synthetic tannin), which is used in the Alter Ego system in order to inhibit the silk from taking up the direct dye. Unfortunately, I don't have any idea as to what chemical, specifically, the syntan may be, and the exact chemistry is not at all clear. There are many different chemicals that are described as syntans. Presumably the syntan in the Alter Ego system is included in their expensive proprietary dye fixative liquid.

The solution for the opposite problem, how they prevent the acid dyes from coloring the cellulose fiber, depends on the choice of acid dyes. Some acid dyes will stain cellulose fibers significantly; some dyes can even work as both acid dyes on protein fibers, and as direct dyes on cellulose fibers. There are other acid dyes that do not stain cellulose fibers much at all. The Alter Ego acid dyes must be drawn as much as possible from the latter group.

I must say that I prefer a chemically simpler example for dye demonstrations to introductory chemistry classes. Proprietary ingredients such as the Alter Ego fixative cannot be described in any detail, because we simply don't know exactly which chemicals are included in them. I can show you a drawing of the exact mechanism of the dye reaction between a fiber reactive dye, such as a Procion MX dye, and the textile fiber; I can't do that for a direct dye or an unidentified acid dye.

Interestingly, you can dye protein and cellulose fibers two different colors with the same mixture of Procion MX dyes, in many cases, because some of the Procion MX dyes react faster than others do with cellulose, while others do the opposite. For example, if you use a mixture of Colour Index reactive yellow 86 (also known as Procion yellow MX-8G, or Dharma's Procion Lemon Yellow) and Colour Index reactive blue 163 (also known as Procion reactive blue MX-G, or Dharma's Procion Cerulean blue), the color produced on cotton is an aqua color, while the color produced on silk is more of an emerald green.

For more information, see the following:

• "Dyeing silk/rayon blends two different colors"
• "Alter Ego dyes"
• "Acid dyes for dyeing silk but not cotton"
• "Chemical Reaction for a Dichlorotriazine Dye With Cellulose"

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