Web www.pburch.net
Paula Burch's All About Hand Dyeing
Overview Fiber Reactive Dyes Direct Dyes All-Purpose Dyes Acid Dyes      Food Coloring      Lanaset Dye      Acid Levelling (Kiton) Natural Dyes Vat Dyes Disperse Dyes Basic Dyes Naphthol Dyes Fabric Paints
Index How to Dye with
    Fiber Reactive Dye
How to Tie Dye How to Batik Low Water
    Immersion
Dip Dyeing Washing Machine
    Dyeing
How to Tie Dye
    with Kool-Aid®
How to Tie Dye with
     All Purpose Dye
How to Dye and
    Paint Fabric
    with Light
cellulose fibers:     cotton     rayon and
     bamboo
protein fibers:     silk     wool synthetic fibers:     acrylic     nylon     polyester     spandex other materials...
acetic acid alginate ammonium sulfate baking soda citric acid ludigol mordants salt soda ash sodium silicate temperature synthrapol urea vinegar water softener
Index Batik Mandalas &
    Peace Signs
LWI dyeing Watercolor Rainbow
    Drip-dyes
Tie Dyeing Spray Dyeing Fabric Paints and Markers
The Dye Forum Book Reviews Find A Custom Dyer Old Q&A Blog Blog of Questions
     & Answers (new)
Search Contact me Link here About This Site
Where to Buy
    Dye & Supplies
Mailing Lists Other Galleries Other Informative
    Sites
Additional Links
Index General Dye
    Questions
Fixing Dye Synthetic Fibers Color Choice Dye Auxiliaries Bleaching and
    Discharging
Safety Procion Dyes Acid Dyes Problems Tying Miscellaneous
Facebook: All About
    Hand Dyeing
Twitter @HandDyeing Google+
Procion MX Dyes Jacquard Acid Dyes Other Dyeing
    Supplies
Fabric Paints, Dyes,
    Books, and DVDs

You are here: Home > All About Hand Dyeing > FAQs > Mordants

Advertisements

Books about using Mordants and Natural Dyes

Advertisements

Colour for Textiles
by Wilfred Ingamells

Never reuse a dyepot for cooking food.

Aluminum or cast iron pots may interfere with the color of your dye.

(Also see About Natural Dyes.)

What's the difference between mordants and other chemical assistants used in dyeing?

Sodium carbonate is not a mordant! Neither are vinegar or salt. A mordant is a metal ion which attaches to the fiber, usually by being boiled together for a length of time. A dye which has no natural attraction to the fiber can then attach to the metal ion. Most but not all natural dyes are mordant dyes, which require the metal ion to be in the fiber in order for them to have any attraction to the fiber. There are also some synthetic dyes that are mordant dyes.

Mordants include alum, chromium, copper, iron, and tin. Some of these metals are quite toxic and hazardous, in addition to be environmentally damaging. Chromium is the most hazardous of mordants. The hexavalent form of chromium, in potassium dichromate, which called for in some recipes, is a known human carcinogen. Alum is the least toxic of the mordants, though it can be irritating and should be used with care.

Tannic acid is another important mordant, a large, complex, metal-free molecule, used mainly in dyeing cellulose fibers, such as cotton. Tannic acid can be obtained from many plant sources, such as the galls on oak trees. A typical recipe for using tannic acid as a mordant calls for boiling cotton first with alum, then tannic acid, then alum again, each in a separate boiling water bath, followed by boiling with the mordant-requiring dye. I think that the alum attaches to the cotton, the tannic acid attaches to the alum, and the dye attaches to either the tannic acid or to another alum ion attached to the tannic acid. This is much more complex, and much less resistant to washing out, then the bonds formed by reacting a modern synthetic fiber reactive dye directly with the fiber.

Most synthetic dyes have no requirement for mordants. Fiber reactive dyes, such as Procion MX dye, have no need whatsoever for a mordant, because they form chemical bonds directly to the fiber. The dyeing process for these other dyes does make use of other chemicals, but not mordants. In some cases a mordant will improve the washfastness of an acid dye on wool, but there is no need to use a mordant with most synthetic acid dyes.

A low pH is useful for dyeing protein fibers such as wool, and a high pH is useful for dyeing cellulose fibers with reactive dyes. In neither case is this achieved by using a mordant. Instead, pH-adjusting chemicals (which are NOT mordants) are used, such as sodium carbonate or vinegar, though they have opposite effects from each other and are used on different fibers.

An acid such as vinegar or citric acid is used as an auxiliary chemical to reduce the pH of the dyebath for dyeing with acid dyes, but acid is not in itself a mordant. It is a coincidence that some chemicals that are used as mordants, such as tannic acid, have the word 'acid' in the names; it reflects an unrelated aspect of their chemical structures. Vinegar and citric acid, like sodium carbonate, are not mordants, though people who do not understand dyeing sometimes refer to them as such. Acids work as dye auxiliary chemicals by reducing the pH of the dyebath to allow the protein fibers to ionize, which aids in allowing them to form hydrogen bonds to the dyes.

Sodium carbonate is a chemical that is used to increase the pH of the dye bath. A high pH causes the cellulose molecule to be deprotonated in order to form a cellulosate anion, which then can attack the fiber reactive dye, after which a permanent covalent chemical bond is formed to attach the dye to the fiber. Deprotonating cellulose with a high pH does not work for dyeing cellulose with other classes of dye. There is little or no advantage in using soda ash for another class of dye. Soda ash will not improve the attachment of, for example, an all-purpose dye to cotton.

You can see a drawing of the chemical reaction between a dichlorotriazine dye, Procion Red MX-5B, and a cellulose molecule, on my dyeing Q&A blog entry for May 19, 2005 (click on this link).

Advertisements


Back to list of FAQs

 Home Page     Hand Dyeing Top     Gallery    About Dyes    How to Dye    How to Tie Dye    How to Batik    Low Water Immersion Dyeing    Sources for Supplies    Book Reviews    Other Galleries    Groups    FAQs     Custom Dyers    Forum    Q&A blog    link here    search    contact me  

Much of the material on this page was originally published in my All About Hand Dyeing Q & A blog, on January 21, 2007.

All of the pages on this site are copyright ©1998‑2017 Paula E. Burch, Ph.D.

Page created: January 22, 2007
Last updated: December 29, 2007
Downloaded: Saturday, August 19, 2017


Mordants