Name: Sharon
Message: I worked for many years as a Histochemist and am now a tapestry weaver wanting to dye my own wool.  I cannot find information as to the exact meaning of "fiber reactive dye" and how it differs from an "acid dye".  Also, there doesn't seem to be a correlation between "MX" codes and certified index numbers.  I would like more scientific information re the mixing of the colors.  Procion dyes seem to be different with each company.  

Try this page, "About Fiber Reactive Dyes":

"Fiber reactive dye is the most permanent of all dye types. Unlike other dyes, it actually forms a covalent bond with the cellulose or protein molecule. Once the bond is formed, what you have is one molecule, as the dye molecule has become an actual part of the cellulose fiber molecule. "

There is a great deal of information about different fiber reactive dyes on that page. Note in particular the table at the bottom on the right side.
Acid dyes bond to textile fibers in a different, less permanent way. For more details, see "What kinds of chemical bonds attach dyes to fibers?":

"The attachment between acid dyes and the protein fibers that they join to are the most complex of all. Proteins are made of up to twenty different amino acids, each of which has a different side chain. At different pHs, different dyes can form rather strong hydrogen bonding to various of these side chains. Many acid dyes contain a sulfonic group, or, in some cases, a carboxylic group, which can form a strong 'salt linkage' to a basic group in the wool molecule....A salt linkage is an ionic bond between fixed ions of opposite charges, due to Coulombic interaction."

Also see "About Acid Dyes", and the various pages on my site about specific classes of acid dyes.

You may also be interested to see my page showing chemical structures for Procion MX dyes, and compare them to acid dyes, as for example on the page "What is Kool-Aid colored with? Is it colored with Procion dyes?".

Note that Procion dyes, both Procion MX dyes (the dichlorotriazines) and Procion H dyes (the monochlorotriazines), can be used as acid dyes if they are used according to an acid dyeing recipe, on a protein fiber such as wool or silk, or on nylon, when used with heat and an acid such as citric acid or vinegar. (See Fiber reactive dyes on protein fibers.) When Procion dyes are used with acid, they attach via hydrogen bonds and/or salt linkages in the colored, chromophore section of the dye molecule, not via the more permanent covalent bonds formed by the reaction between the fabric and the dye's reactive section. In order to get a fiber reactive dye to act as a true fiber reactive dye on cotton or any other cellulose fiber, you must use a high pH, such as with soda ash.

Only ten to twenty of the available Procion MX dyes are pure, unmixed, single-hue dyes. The remainder are mixtures and therefore have no Colour Index names. Which single-hue Procion dyes your dye supplier sells, and what names they are sold under, varies according to your choice of dye supplier. The MX codes and Colour Index names are listed, along with the common names and catalog numbers at a number of different dye suppliers, on my page "Which Procion MX colors are pure, and which mixtures?". I find the Colour Index names (e.g., "reactive orange 4") more useful than the Colour Index numbers (e.g., "CI 18260").

All of the single-hue unmixed Procion MX dyes are the same regardless of where you buy them, but each dye company also sells proprietary mixtures, which are completely different at different retailers, even if they have the same common name (e.g., "chocolate brown"), plus a few manufacturer's mixtures, which are the same everywhere unless they have been replaced by proprietary mixtures. Single-hue unmixed dyes have MX codes, but so do the manufacturer's mixes and, in a few cases, the proprietary mixtures that have been introduced to replace a manufacturer's mix during a period of low availability. Here's a link to an explanation of how to interpret the original meanings of MX codes.

There are far more acid dyes in the world than reactive dyes. I list Colour Index names on the "Leveling Acid Dyes" page, on "Which Washfast Acid colors are pure, and not mixtures?", and on "Lightfastness of Different Types of Dyes", among other pages.

When you use Procion dyes on wool at  a low pH, they do not bond as fiber reactive dyes. However, there are true fiber reactive dyes that are formulated to react with wool at low pHs. As a result, they are more washfast than acid dyes. See "About Lanaset Dyes", and "Vinyl Sulfone (Remazol) Fiber Reactive Dyes" . The latter work at a wide range of pHs on protein fibers, but can be used only at high pH on cotton and other cellulose fibers.

I would like to encourage you to join the Dye Forum. It's an ideal place to ask and discuss more detailed questions.

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