Homemade iron mordant: what factors affect mordant quality?

Making an iron mordant is simple – get some pieces of iron, preferably rusty, put them in a jar and cover with vinegar. Let this sit for a couple of weeks, or until the liquid changes colour, and then use. (I go deeper into this method in my eco-printing ebook, Gum Leaf Alchemy).

But there are different factors affecting the quality of iron mordants. Here’s three pieces of cotton cut from the same piece of fabric and eco-printed with the same eucalyptus leaves, but with quite different results:

The difference between each sample was the quality of the iron mordant used. Let’s take a closer look at each.

Sample 1: A poor quality eco-print 

The mordant on this piece had been diluted with water a few days before eco-printing. It was a strong mordant that I was trying to dilute. The results are very pale and fuzzy:

The problem is that the vinegar is a vital component of the mordant because of its acidity. When water is added to iron mordant, it raises the pH and changes the iron from a dissolved form to a solid form. This is sometimes quite visible, it looks almost like the mordant has curdled. In this state, during the mordanting process it stays suspended in the liquid rather than bonding to the fabric.

This process is not immediate (otherwise it would not be possible to put iron mordant into water to mordant fabric). But it will be visible if you save any leftover mordanting water for a few days or longer, especially if it was quite strong. You will be able to observe the iron separating into small clumps and settling at the bottom of the container. 

So, the moral is don’t add water to your mordant. If you have an overly strong mordant, you can either use less of it or add vinegar to dilute it.

Sample 2: A mediocre eco-print 

The mordant on this piece was very old, and had been soaking for over 2 years. Although the mordant itself looked great, very dark and strong, the prints are fairly washed out, without the crisp detail I sometimes get on cotton:

The reason for this is that vinegar will lost its acidity over time, creating a similar problem to adding water to a mordant. Ideally you will be using your mordant regularly, and topping it up with more vinegar each time. If you have a very old mordant (unused for 6 months or longer), try adding new vinegar, letting it rest at least a few days before you use it again. If you still get disappointing results, you may need to make a new mordant instead.

So here the lesson is that the colour and darkness of the mordant won’t necessarily predict results. And that it is important to keep topping up your mordant with vinegar.

Sample 3: A high quality eco-print 

This last piece was made from a mordant that was only 2 months old but contained a lot of rusty metal so was a good strong colour. There is crisp vein detail on each leaf and lovely blue dots dappled across the brown leaf prints:

These are optimal results for eco-printing on cotton – crisp, detailed and dark. The pale prints still look nice but will fade much faster.

This sample shows that iron, vinegar and the right amount of time (not too little, not too much) are all you need to create a great iron mordant.

Other iron mordant considerations 

Often people think that the brightness or paleness of a print is caused by using more or less mordant. But actually, other factors are far more important. How well the fabric was scoured, how much pigment is in the leaves, and the quality of the mordant can all drastically impact the results you get. The fabric will only absorb a certain amount of mordant, and a small amount is surprisingly potent. So even when using homemade mordants that aren’t measurable, it is not easy to drastically over- or under-mordant your fabric.

One final mordant variable is when you have used up the liquid of a mordant, but have iron sludge at the bottom of the jar. Once you top it up with fresh vinegar, you need to let it sit for a few days or longer otherwise it will also give pale results.

So if you have been getting poor or mediocre results when eco-printing on cotton, I encourage you to consider whether your mordant might be the reason why. If you need more help with getting great results on cotton, check out my eco-printing ebooks for in-depth information about every step of the process.

Pin this information for later:

Eco-printing and shibori dyeing on wool

In Week One of my eco-printing ecourse, we explore how to combine eco-printing and shibori dyeing on wool. Shibori is a Japanese dyeing technique, where you fold or tie up the fabric in order to create resists. Then you submerge the fabric in dye. The resist area stays plain, while the exposed area picks up the dye. This produces a pattern. By placing leaves inside the areas of resist, you can get organic leaf prints surrounded by geometric patterns of solid colours. Here is a vest dyed in a similar way to what we explore in the ecourse:

To create this, I used eucalyptus leaves for the eco-printing, and created a dyebath of eucalyptus sawdust with iron mordant to darken it.

A piece of woollen fabric dyed with a dark grid, interspersed with bright orange leaf shaped prints

Living Colour: Eco-printing on Cotton Ecourse

I am delighted to announce the release of my new ecourse, Living Colour, which explores different techniques of eco-printing on cotton. It’s my way of lovingly guiding you through the process if you are too far away to attend a workshop. We’ll be creating our own wardrobe of living colour, using the natural dyes in plants.

Learn how to eco-print on cotton with Louise Upshall from Gumnut Magic

Eco-printing newbies are welcome as we will cover the basics of preparing leaves and fabric and rolling bundles. But we will also explore some things that I haven’t shared in any workshops yet, such as combining eco-print and shibori methods, and using a soy binder. You can view the trailer and curriculum or register now over at learn.gumnutmagic.com

Making natural paints and inks from plants

I’ve been making an exciting foray into the world of natural paints and inks. It’s not so different from natural dyeing really. You can use the same dye plants but just create a really strong dye bath by using a higher proportion of plant material to water. If the colour isn’t quite strong enough when you strain it, simmer it down until you reach the desired effect.

Natural ink made from onion skins and marigolds

For my first paints, I’ve gone with some classic dye plants. Above is red onion skin, brown onion skin and marigold flowers. I cooked these for about 2 hours, but the beauty of it is that there is no right or wrong length of time, just different colours and strengths. A lot of plant dyes will brown if you cook them at too high a heat though, so keep it at a low simmer.

Onion skin ink and iron on watercolour paper

Here I tried painting circles on watercolour paper with the red and brown onion skin paints, and adding in a drop of iron mordant (rusty iron dissolved in vinegar). It is so beautiful watching the plant dyes and the iron mix and blend. And I love having a new use for the mordants that I already use for my natural dyeing.

Avocado seed paint/ ink paper tests by Gumnut Magic

Next up was some avocado seed ink. The gorgeous peachy colour at the top was made after a short amount of cooking. The right sample is a simple brushstroke of the final colour, a beautiful earthy pink. The middle sample shows how beautifully it spreads on Japanese paper. And the bottom left two pieces have some iron mordant dropped in to modify the colour- which creates patches of gorgeous lavender purple and smoky blue.

After cooking, you do need to strain the liquid very well to remove any small particles of plant material. Use a coffee filter, or a piece of fabric folded over several times and placed within a metal strainer. Then you can use the paint as-is, or add a binder such as gum arabic to give it a more painterly consistency. Add a clove to each jar of paint or keep them in the fridge to prevent moulds from developing.

Making natural paints from onion skins, avocado seeds and marigold flowers

Here is my collection of paints so far. They look much darker and sometimes even a different colour in the jar to how they turn out on paper.

If you want more inspiration on making your own natural paints, I highly recommend the books Make Ink by Jason Logan and The Organic Artist by Nick Neddo.

If you want to come back to this idea later, you can pin the image below.

Use onion skins or marigold flowers to make paint or inkJ

Eco-printing on paper video tutorial

Here’s a video tutorial I made about eco-printing on paper using a rusty can. I love this method because it is easy to get interesting prints with most types of paper and leaves, although I have used some of my favourites for this demonstration.

This is one of the methods I share in my eco-printing on paper ebook, Plant Poetry, along with lots of information about plants, papers and bundling techniques to try.

If you just want to watch a quick preview of the whole process, check out this short video:

I hope that this inspires you to get creative with the plants around you. Have fun experimenting!

A wasteland dress

Piecing together a tattered wasteland dress- Gumnut Magic

I’ve been working on something a little different. Sculpting this dress from many years worth of naturally dyed fabric scraps. Beautiful leftovers from wrapping bundles, with so many unique marks and memories. Using what I have, embracing imperfection and delighting in texture. 

Gumnut Magic wasteland dress

Eco-printing on paper with waratah flowers

Here’s an old experiment that I haven’t shared on here yet. Waratahs are native Australian plants with luscious, bright red flower heads.

Aged Australian waratah flower

I had a beautiful waratah that was looking a bit old. It had turned purple and the individual flowers were starting to fall off. So I gathered them up and decided to try eco-printing on paper with them.

Waratah flowers for eco-printing on paper

First I sprinkled them over a small piece of watercolour paper.

Eco-printing on paper with a rusty tin

Then I wrapped and tied this around a rusty metal tin.

Rusty tin flower eco-printing by Gumnut Magic

I cooked the tin in simmering water in a dye pot for about half an hour then let it cool before unwrapping it to see what colours and patterns had emerged.

Rust and waratah flower eco-prints on paper

The shapes of each flower showed up clearly, outlined in dark black where the natural dyes have interacted with the rusty tin. The rust  also created lovely orange speckles across the background.

Using a rusty tin is one of my favourite methods for eco-printing on paper. It helps you get striking results even if your plant materials don’t contain much dye. This simple technique can be adapted to any leaf or flower that you want to try (as long as they are not toxic, of course!)

Waratah leaf eco-printed on cotton

I have also experimented with using waratah leaves for eco-printing on cotton. I was able to coax out a small amount of colour, but I probably wouldn’t try it again as there are many other types of leaves that give stronger results.

Waratah flowers and rust eco-printed on paper, by Gumnut Magic

Wrapping eco-print bundles

Here’s a quick video of how I wrap and unwrap eco-print bundles. Unlike many eco-printers, I don’t wrap around a stick or other firm object. I prefer to just fold the bundle in on itself and then tie tightly. This creates a semi-flexible bundle that fits easily into the dyepot.

This piece was mordanted with iron and eco-printed with eucalyptus leaves, using the method described in my ebook Gum Leaf Alchemy.

How long to boil eco-print bundles

When I first started eco-printing, I boiled my bundles for 3 hours. I got good results, so I kept doing this. But one day I noticed that after a short amount of boiling the leaves had already produced a lot of beautiful colour.

So I decided to take a more systematic approach to working out the optimal length of boiling. I made up a batch of small bundles using leaves from 3 different eucalyptus varieties on pieces of the same pre-mordanted cotton. I set them to boil, then removed them at 15 minute intervals.

I was suprised to see that there wasn’t much difference between the bundle that had been boiled for just 15 minutes (left), and the very last one which was left in for 1 hour and 45 minutes (right).

Comparing different boiling times for eco-print bundles

The colour of the leaves on the top sides did shift from brown to blue with longer boiling times, but the centre green and botton brown leaf prints didn’t really vary. The blue band on the right side print is from the piece of dowel that the bundles were wrapped around. This band got progressively darker and bled more the longer that each sample was boiled for, because wood has its own tannins.

Even though much of the dye has already emerged after 15 minutes, I do cook my bundles for longer, to ensure that the maximum amount of colour is transferred to the fabric and to really give it time to set. I find that about 1 hour is a good length of time when eco-printing on cotton. It’s enough time to get strong prints, while being mindful of energy use.

A comparision of cooking times for cotton eco-print bundles

Shibori eco-printing on cotton

Following on from my recent post about combining shibori dyeing and eco-printing on wool, here are some similar effects achieved on cotton. I really enjoy combining organic eco-prints with geometric grids or lines from shibori dyeing methods.

Liquidambar leaves eco-printed on cotton with iron and alum mordants

This pattern was created by folding the tshirt up into a small bundle, adding liquidambar and Japanese maple leaves as I went. Then I tied it tightly with string and submerged it in a dye bath of eucalyptus bark and iron, cooking it for about 1 hour. The fabric was mordanted with homemade iron and alum mordants, following the instructions in my ebook, Gum Leaf Alchemy.

Cotton naturally dyed with eucalyptus leaves and bark

Here is a close up of a similar pattern, this time with eucalyptus leaves and an iron mordant. The large section of lines show which part of the tshirt ended up on the outside of the bundle, wrapped tightly with string. There are smaller sections of lines where other parts of the tshirt were also on the outside of the bundle, because of how it was folded.

Creating a geometric grid overlaid with eucalyptus leaf eco-prints

This long-sleeved tshirt was also folded up, but into a smaller bundle which was pressed between two square pieces of hardwood. This helped to create a very even, geometric pattern to contrast with the organic shape of the leaf prints. This piece was also mordanted with iron and alum.

Rose leaves eco-printed on cotton by Gumnut Magic

This piece of fabric was mordanted with iron, covered in rose leaves and folded into large squares. I pressed the fabric between 2 tiles, clipped the tiles together then submerged the bundle in a dye bath and cooked it.

If you would like to come back to this idea later, you can pin the below image.

Examples of cotton clothing naturally dyed with 2 different techniques: shibori and eco-printing