Eco-print experiments – Gumnut Magic

Homemade iron mordant: what factors affect mordant quality?

September 13, 2019 March 23, 2020

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:

How long to boil eco-print bundles

February 19, 2019 March 23, 2020

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).

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.

Good leaves to use for eco-printing: experiment two

May 8, 2017 March 23, 2020

I get asked a lot if the method I described in my ebook will work for non-eucalypts. These samplers are a good example of the results you can get using different types of leaves. Following on from the first experiment I documented, these leaves were left to soak for about 2 months before I used them, and it really made a difference! Some of the leaves printed better than others, but I really enjoyed seeing how so many different types of leaves, some native to Australia and some introduced species, can produce such clear and beautiful prints.

I sandwiched the leaves between two different pieces of cotton, to observe the difference in the prints produced from each side of each leaf:

These prints are of the ‘sky-facing side’ of the leaves (where applicable). Most produced a lot of colour, and the leaf outlines and veins are crisp and clear. They are printed onto a yellow woven cotton, which has created beautiful green hues for many of the leaves, in contrast with the bluer prints below.

These prints are of the ‘earth-facing side’ of each leaf, on a white stretch cotton. Some still printed very clearly, especially the maple, oak and blackberry leaves, while others produced only faint outlines.

Mordanting with blood

February 25, 2017 March 23, 2020

I’ve been curious about mordanting with blood ever since I read India Flint’s passing reference to it in Second Skin. I’m not a squeamish person and I have ready access to a cruelty-free form of blood each month with my menstrual cycle, so I thought I would give it a go. I wondered if it would give similar results to other protein mordants, or whether the particular properties of blood would effect the results.

To prepare the fabric, I simply soaked it for about an hour in the water I had soaked my cloth pads in. Then I lay it flat to dry and let it set for about a week before eco-printing.

The mordant definitely worked, although the prints were fairly light. Next time I would try to use more blood and soak the fabric for longer to create a stronger mordant. I might also try a series of ‘dipping and drying’ as is done with soy mordants, and see if this gives more vibrant results.

Eco-printing on wool versus cotton

February 12, 2017 March 23, 2020

I prefer eco-printing on cotton rather than wool for a few reasons. Cotton clothing is easier to find at op-shops, and in a wider range of styles, than wool. Upcycling clothing that already exists feels like the most ethical way I can do a lot of eco-printing, so it makes sense to go with what is readily available. I also love the wider range of colours and textures that I can get on cotton. Eucalyptus leaves mostly print solid colours on wool, whereas prints on cotton often have extra details like blue dots.

When I was writing my ebook, I wanted to show the difference between wool and cotton eco-prints. I did a range of small samples with the same leaf sandwiched between one piece of wool and one piece of cotton. It was so interesting to see the different colours that came from the exact same leaf on the different types of fabric. All of these photos show the wool on the left and the cotton on the right.

Some of the mordant on the cotton did transfer somewhat onto the wool, seen most starkly in the dark borders around the leaves and gumnuts above, so I can’t expect the same results with these leaves on unmordanted wool.

I was especially excited to get some more insight into which leaves dye best on wool. Lots of the eucalyptus leaves here in the Blue Mountains dye quite pale, especially without any mordant. I noticed that I got beautiful bright oranges from silvery-blue leaves, while the greener leaves dyed pale yellows on the wool. Almost all of my local gumtrees have dark green leaves, so I guess it’s lucky I’m not often wanting to get bright prints on wool!

Even more interesting, the leaves that dyed orange on wool consistently dyed brown on (iron-mordanted) cotton, while the leaves that dyed pale yellow on wool dyed blue or blue-green on cotton. I know that some green eucalyptus leaves do dye brilliant reds or oranges, but my local ones don’t seem to have the right chemical components for that.

I still have a lot that I want to investigate about different types of gumleaves and what factors influence which colour they dye, but this was certainly a useful experiment and a very good way to get to know more about my local leaves.