From time to time I get questions from my ebook customers, wondering why they have gotten pale or disappointing results when eco-printing on cotton using an iron mordant. There is no simple answer, because there are a lot of different variables that can affect results. In this post I will discuss some of the major variables, as well as ideas for troubleshooting the cause of pale prints.
When we eco-print, we use leaves, fabric and mordant. Each of these has its own set of potential problems.
Troubleshooting fabric variables
Fabric naturally contains oil and waxes that act as a barrier for natural dyes, preventing them from binding to the fabric. If you want to use new fabric, you need to scour it. Scouring is a form of deep washing that strips out the oils and waxes. Insufficient scouring can cause pale results. Make sure you follow scouring instructions carefully and rinse well afterwards with hot water. You can find instructions for scouring in my Gum Leaf Alchemy ebook , Intro to Cotton ecourse , or through a web search.
A simpler option to use old, well washed fabric. Often this takes up natural dyes even better than scoured fabric.
Another fabric problem can be not wrapping bundles firmly enough. The leaves need to be pressed firmly into the fabric, otherwise the dye will seep out into the water and cause pale, patchy prints, rather than being absorbed directly where it is touching the fabric, in a perfect leaf shape.
Troubleshooting leaf variables
There are two major leaf variables that can cause pale results. First is the leaf itself and whether it actually has enough natural dyes in it. Some plants are great for eco-printing with and others just aren’t. And a particular genus may in general be good for eco-printing, but that doesn’t mean that every species in that genus will be. For example, some eucalyptus species will produce vivid orange or red prints on wool, while others don’t even create a print. And even species that usually give good results can be affected by growing conditions, weather and rainfall, as well as the time of year that you pick the leaves.
The second leaf variable is how it has been collected and stored. In my ebooks and ecourses, I recommend collecting fresh leaves and soaking them in water for a few days or weeks, to remove the water soluble tannins that can cause bleeding on iron-mordanted fabric. Soaking the leaves makes some of the dyes more available, so you get brighter and clearer results that with fresh leaves. But soaking them for too long can also cause pale results.
I recommend doing your own tests – compare fresh leaves with some soaked for a few days, a week and 2 weeks, all eco-printed on the same piece of iron-mordanted fabric and cooked for the same length of time. This will help you begin to see what works best for your local leaves.
I explore all of these leaf factors more deeply in my ebook, The Leaf Guide.
Troubleshooting mordant variables
Homemade mordants can be a little tricky, because they are all different strengths and the quality can vary, depending on what metal you used for it and how long it has been brewing. In general, as long as your mordant changes colour as the iron soaks in the vinegar, it is usable.
To test the quality of your iron mordant, try to control the other variables as much as possible. Use old, well washed cotton and some reliable leaves like rose and Eucalyptus cinerea. I recommend using them fresh, so you don’t accidentally use leaves that have been soaked for too long. Press your bundle between tiles and secure with clips, to ensure good pressure. Cook on a low boil for 1 hour, then let cool in the pot.
If you get strong results, you will know that your mordant is okay, and you can start experimenting with soaking the leaves for different lengths of time and using other fabric.
If you get pale results, it tells you something is probably wrong with your iron mordant. One possibility is that it is too old – iron mordant gets weaker over time as the pH changes. Another possibility is that the piece of metal you used wasn’t the best for making mordants with – try to find a very rusty piece of iron to make a new mordant with.
Does the amount of mordant matter?
Homemade mordants vary in strength, so it is not possible to give precise instructions like ‘use 4% of the Weight Of Fibre’. Some people worry that they have used too little or too much. Don’t be too worried about the amount though – the fabric will only absorb some of what is in the mordant bath, and it is quite a forgiving process.
A small amount is surprisingly potent, and it is rarely the case that people haven’t used enough. If you are doing a large batch of mordanting, just make sure that you add a small amount more after soaking each piece of fabric, to replace the mordant that it has absorbed.
Using too much mordant can be a problem however. If your fabric yellows significantly after being in the mordant bath, you have used more that necessary. Try to flush some off by soaking it in plain water. Too much mordant will damage the fibres and make them tear and break down much more quickly.
Enjoy them as is. Let go of the idea that eco-prints have to look a certain way, and just enjoy what you have received from the plants.
Re-print them: re-mordant your fabric and add a new layer of leaf eco-prints. This is also a good thing to do when eco-prints have faded from sun exposure. Fabric generally takes up natural dyes much better the second time.
When doing natural dyeing or eco-printing on plant-based fibres such as cotton, you need to prepare the fabric with something to help the plant dyes adhere. This could be mordants such as metals and/or tannins. Or you could use a protein-rich binder such as soy milk, cow’s milk, eggs or even blood. These emulate the results that you will get dyeing protein fibres (wool, silk, leather).
For ethical reasons, I only use cow’s milk to prepare fabric when it would otherwise be going to waste. It doesn’t seem reasonable to buy it for this purpose when many people are starving and the dairy industry is horrific. But I have a friend who occasionally brings me bottles from their workplace that are close to their use-by date and were going to be thrown in the bin. Dumpster diving is also a good way to find wasted milk and put it to good use.
How to prepare fabric with cow’s milk
Scoured cotton, linen or other plant based fabric
A large pot or bucket
1 bottle of cow’s milk
Step one: add water to your milk at a ratio of 1:1. Pre-wet your cotton fabric (so it will absorb evenly) and add it to the milk. There should be enough space for the fabric to move freely. Let it soak for about half a day, stirring occasionally. This is best done on a cold day or in a very shady spot or else the milk will quickly get smelly and this smell will remain in the fabric even after dyeing. I soak fabric for less time in cow’s milk than when using soy milk, because it does tend to go bad faster (especially when it is already close to the use-by date).
Step two: remove the fabric, squeeze out the excess milk and put it in your washing machine on a spin cycle. Then hang to dry. Putting it on a spin cycle means that there won’t be milk dripping down the side of the fabric as it dries, which would show up as streaks when you dye it.
Step three: if your milk is still good, add the fabric back in just until it is saturated, then remove and put through the spin cycle and dry again. Do this process twice. Adding extra layers strengthens the binder, and it is done in quick dips so that the previously adhered milk won’t have time to come off. These extra steps can be omitted if your milk bucket is getting too smelly- you will still get good results from one round of soaking.
Step four: once your fabric is dry, leave it to cure for at least a week before dyeing it. Again, this strengthens the binder and helps it adhere strongly to the fabric. Then dye or eco-print with it as desired.
The difference between protein binders and metal mordants
This picture illustrates the difference between protein binders and metal mordants. The top piece of cotton was prepared with cow’s milk. The bottom piece was mordanted with iron. Both pieces were eco-printed with the same species of eucalyptus leaves. On the milk binder, the leaves have printed a bright reddish-orange. This is similar to the results these leaves give on silk and wool, which is unsurprising because protein binders make plant fibres dye similarly to protein fibres. On the iron mordant, the leaves have printed olive-green and have some speckles and vein details. I find that iron mordants are great for bringing out details, while protein binders give flatter results but sometimes more vivid colours.
I hope this has been useful for you and gives you a way to make use of milk that would otherwise go to waste. Feel free to pin the image below to return to this information later.