Combining iron and alum mordants for eco-printing

Although iron is my trusty favourite mordant- easy to make, relatively low toxicity, and easy to dispose of- I have been experimenting with alum lately. My first results of eucalyptus on alum were not very promising. Fluro yellow is not my favourite colour. But then I tried double-mordanting, combining both iron and alum. I hoped that the saddening effect of iron would help tone down the brightness of the alum and bring in more subtleties. And it worked beautifully!

The alum has brought out these beautiful oranges and yellows from the eucalyptus leaves, while the iron gave more depth and detail:

Double mordanted with alum and iron

The colours vary according to how much alum and iron are used, and the particularities of each piece of cotton too. It is important when eco-printing to be open to the different possibilities and to embrace the results you get. Each print is a gift from the leaves, so be grateful.

How to mordant cotton

This onesie was bit of a failure originally. It had pale, faded grey prints, probably from not being scoured properly. The alum and iron mordanting prepared it well for a second round of eco-printing, and it was transformed into one of my favourite pieces so far. Aren’t the gumnuts exquisite?!

Mordanting cotton with alum and iron

To do this double mordanting, I scoured the cotton, gave it a short dunk in one mordant, let it dry and cure, then dunked it in the other. Then I eco-printed the fabric in my usual way, using the instructions I share in my ebook Gum Leaf Alchemy.

Combining alum and iron mordants to eco-print on cotton
Combining alum and iron mordants to eco-print on cotton

If you’d like to learn more, I have a lesson about combining alum and iron mordants in my ecourse, Living Colour.

8 thoughts on “Combining iron and alum mordants for eco-printing”

  1. These colors are beautiful! Are you using your home-made alum mordant or a commercial alum, like potassium aluminum sulfate (pickling alum) or aluminum acetate?

    1. Thanks Wendy. I’ve used both homemade and store bought successfully. I think for this particular one I used Alum Acetate powder.

  2. Billie-Leigh Dale

    Hello there,

    Your results are amazing. How long did you do the dunking for? I leave my fabrics to soak in aluminium acetate for 24 hours… How should I do with the iron added?

    1. I let them soak in one mordant for a few minutes, dry, and then soak in the other for a few minutes. But if you get good results from a long soak in aluminium acetate, you can do that, let it dry, then do a quick soak in iron so it doesn’t dislodge the alum already on the fabric.

  3. Thanks for sharing your knowledge . I am just starting to investigate this exciting field so all tips greatly appreciated

  4. Are using calcium carbonate at all in this process ? It’s suppose to help Alum acetate bind to fabric. But if you are using iron dip perhaps it’s not necessary?

    1. No I don’t use calcium carbonate, I find that the iron and alum acetate alone bind sufficiently and give me the results I want.

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