Iron as a pre-mordant
In all of the natural dyeing I’ve been doing (or hoping to do!) in the last little while, I read a little about using iron as a pre-mordant instead of alum. In Rebecca Burgess’ Harvesting Colour: How to find plants and make natural dyes, she notes that while alum is used for most of recipes in her book, iron is useful in several.
“… several recipes, including fennel, sheep sorrel, and French broom, recommend using iron to prepare your fibres before dyeing, because it has a tendency to create deep green colours from dye baths that might otherwise yield yellow.”
Rebecca has instructions for using powdered iron or ferrous sulfate from dye supply stores, but also provides a ‘recipe’ for making a solution from rusty objects. Since I’m trying to do new projects with as little of out-of-pocket cost as possible, this sounded great to me, and when we tore down our little mini-shed in the back yard this fall, I ‘harvested’ the rusty nails from the project and saved them for this. The one challenge with this is that you won’t know the percentage of iron to the weight of goods, which might mean a greater challenge getting consistent colour between dye projects.
Rebecca notes that you can pre-mordant fibres immediately before dyeing, or leave them “indefinitely”, though she recommends the best colours come from letting the fibres sit for a week after pre-mordanting, before dyeing. She specifically indicates that this iron premordant is suitable for protein fibres, though other sources have suggested that ‘too much’ iron can break down protein fibres, making them brittle. With this in mind, I don’t know if I want to leave the pre-mordant on my wools for very long before dyeing.
Her specific recipe calls for a 1 gallon container with a lid, 2 handfuls of rusty objects, and 1tbsp of white vinegar for every 1cup of water to fill the container about 3/4 full. With time, she indicates the liquid will turn dark orange.
“During summer months, the process will take from several days to a week; in the winter, due to the colder air temperatures, the process will take several weeks”.
The dark orange liquid is added to the dye pot along with additional fresh water to allow the fibres to move freely. The liquid is heated to 180-200F (below boiling, or 80-90C), and then the fibers are introduced, let sit on the heat for 60-90 minutes, and then rinsed in warm water and hung to dry.
In Jenny Dean’s Wild Colour, she discusses the use of mordanting with iron on vegetable fibres. She writes that while iron can tend to deteriorate animal fibres over time, it has less impact on vegetable fibres. Her recipe for home-made iron liquor includes just putting rusty nails or scrap iron into a glass jar with a lid – fill the jar with two parts water to one part clear vinegar, and let the solution steep for one to two weeks, until the solution turns a rusty-orange colour.
Iron as an after bath dye modifier
In Rebecca’s book she also examines the use of iron as a modifier when used in an after bath. For this, the fibre is introduced to the modifier immediately or soon after the dyebath. She writes that iron can be used to deepen or “dull” (other sources call this “sadden”) the colour.
Rebecca’s ‘recipe’ for this is to fill the pot with the iron-vinegar-water solution (adding additional water if needed so the fibres can move freely), and then heat the solution until it’s just beginning to steam (approx 140-160F, or 60-70C) and let sit for approx 10 minutes. Then let the fibres cool and rinse in warm water before hanging to dry.
She recommends this modifier for Staghorn Sumac specifically, but also notes it for other dye stuff as well.
Iron as a dye for vegetable fibres
In Jenny Dean’s Wild Colour, she notes that the iron liquor can also be used as a dye bath on cotton, and linen. She also suggests that this can even be used on silk as a dye, but cautious against using it as a dye on wool. To use this as a dye, proceed as a mordant, but do not rinse the fibres. Instead, soak them in a hot solution of washing soda made from 2 teaspoons of washing soda for every one liter of water. When the fibres are exposed to air, a light and washfast rusty-orange colour will develop.
My iron liquor
So since the two recipes I found didn’t align at all in terms of recommendations of vinegar to water (1:2 and 1:16), I took this to mean that the ratios weren’t vital to the results… just changing the pH of the water to encourage rust. I put my rusty nails in a brand-new mason jar, added water and vinegar, and then let it sit. A generous foam developed within a few days, and the water became quite tinted orange and cloudy.
After about 2 weeks of steeping my nails – spontaneously my jar cracked – the bottom snapping off, and the entire contents spilled all over my kitchen counter and floor. If my mop is any indication… the liquor would have been successful – everything was tainted a pale orange. Unfortunately my housemate threw out my jar with the notes neatly written on tape, so I don’t know what my vinegar to water ratio was.
So… back to the drawing board.
For a second round, I re-used the rusty nails, and found some steel wool at the hardware store to add to the mix as well. This was put in a plastic ice cream jar, along with a 1:5 ratio of vinegar to filtered water on November 30… and let to steep.
It steeped until February 4 when I did a bunch of dyeing with apple leaves and twigs. (My post about that is coming soon, but you can see some of my previous, unmordanted examples here.)
I had some handspun wool (Shetland Top I think), along with some white linen, tan silk, and tan linen that had been pre-mordant/dyed with oak galls. I had not rinsed the mordanted fibres, so re-moistened them with water, and then I quickly dipped each of the materials into the iron liquor one by one. I knew to not leave the wool in the iron very long.
I was incredibly happy with the results!
The materials were only in the jar for a brief time, and then were rinsed, washed, rinsed again, and dried. While still wet, the silk was very dark, the linen slightly lighter, and the wool a medium grey.
Interestingly, I could not fit all the wool into the jar, so left it sort of variegated – the yellowish tone of the oak gall mordanted/dyed wool, blending with the grey of the modified wool. However, when I did the first rinse, there must have been so much iron in the rinse water that the entire skein was modified! Potent! On close inspection I can kind of see the lights and darks, but I feel this is more because I know it’s there.
I set the fibres aside to dry a bit (puddled in the upturned lid of my dye pot, because I didn’t have space to lay them out on a line) overnight, and then put the damp fibres on a line to finish drying.
The previous picture was taken next to natural light, while this photo of the damp fibres under incandescent light – the tones of the grey aren’t true, but the depth of colour is accurate.
Finally – the finished product. On the left is the handspun wool yarn, and on the right is the commercially woven fabric.
On the top is silk. The original colour was a tan, then mordanted darker tan with the oak galls, and finally a warm charcoal grey.
The middle fabric is a tightly-woven linen. The original colour was a bleached white. This predictably didn’t take as much colour. After mordanting with the oak galls it was a very light tan, and after modifying the colour shifted to a light grey.
The bottom fabric is the most surprising. This is also linen, but was just the scrap of linen I used as a filter for the oak galls. It was originally light tan, the mordant straining made it a darker tan, and the result after the iron is a nearly-black dark grey.
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