How to Use Metal Mordants

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“The Handbook of Natural Plant Dyes” by Sasha Duerr is full of helpful tips and recipes for home dyeing enthusiasts.
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Fig leaves in a stainless steel pot ready for extraction and iron mordanting.

Home dyeing can be a gamble if you are new to the idea, but even if you are experienced in the art, knowing the reaction difference between animal fibers and plant based fibers can be crucial to proper dye absorption. Using The Handbook of Natural Plant Dyes (Timber Press, 2010) Sasha Duerr walks you through using mordants and natural dyes in perfect harmony. This excerpt explains the use and handling of metal mordants.

Metal Mordants

Handle all mordants with care. When working with mordants, always wear gloves and a dust mask. And when working with mordants and heat, keep the mordants and dyes well below the boiling point so fumes aren’t created that you might inhale.

The only metallic mordants we will be working with in this book are alum and iron. These mordants are nontoxic when used in the proper proportions. But they can be irritants and caustic, so work with them carefully to avoid any health hazards. When handled properly, alum and iron are excellent, easy mordants to use, to get longlasting and even dramatic colors.

Using Alum as a Mordant

Alum, or aluminum sulfate, is a substance found in the earth, and has been used as a mordant for thousands of years. Alum will brighten colors and will make many natural plant dyes colorfast. Since some plants love alum, you can often find it at gardening stores in the fertilizer section. And since it is used for pickling, you can usually get it at the grocery store in the spice section. Or try a specialty textile supplier. Alum can help extend the range of colors your plant dye can achieve, often allowing your dye pot to bloom into brighter and more intense color.

Using Iron as a Mordant

When iron (ferrous sulfate) is used as a mordant, it often turns dye colors darker in tone. Iron is an earth-based substance, and we use it in powder form as a mordant material. It can be ordered from dye specialty stores or made yourself; a little goes a long way. Iron can be used as a premordant, but works just as well as an aftermordant. Iron can extend or alter the color from the initial dye bath. Iron usually takes effect very quickly, darkening the color or sometimes changing it completely.

Iron is a natural color modifier. Modifiers are usually applied to the dye bath to alter the color after the initial dyeing has occurred. Some modifiers, like iron, can also be mordants, but most modifiers change the color but do not help bind the color to the fiber unless a mordant has been used first. You can create iron liquid solution ahead of time and store it in clearly labeled in glass jars. One of the first traditional mordants was probably mud with a high level of iron in it. Ancient peoples may have become aware of iron’s mordant abilities when watching leaves fall into iron-rich water and turn black from the chemical change.

Iron mordants should be labeled and safely stored. Iron is generally nontoxic in small doses, but can be potentially harmful and even fatal if swallowed in large quantities, especially by children and pets. Small amounts of iron are all you will ever use with fabric, since certain fibers, like wool and silk, have been known to fall apart over time if they have been treated with too much of this mordant.

It is important to always clean your pots well after mordanting fibers with iron. Iron mordant can leave a residue that can affect later dye baths by creating a duller or modified color, and can create unwanted spots on your fibers or textiles. Even a little bit of iron can cause colors to be more dull or gray versions of a dye color. You will want to keep a dye pot just for iron mordanting.

Use mordants and aftermordants for your home dyeing projects. Read Using Mordants With Natural Plant Dyes for more recipes and tips from Sasha Duerr.

This excerpt has been reprinted with permission from The Handbook of Natural Plant Dyes: Personalize Your Craft With Organic Colors From Acorns, Blackberries, Coffee and Other Everyday Ingredients, published by Timber Press, 2010.