Color with Rust: Making an Iron Mordant
Got any rusty old metal lying around, or know someone who does? All you need is vinegar, water, and some patience and you've got a liquid that will provide a larger, deeper spectrum of colors when used with natural dyes! (Recipe adapted from "Wild Color" by Jenni Dean, a go-to for natural dyers everywhere)
To make this "Iron Liquor" place rusty metal in a jar (you don't need a whole lot, a small handful or a couple larger pieces should be fine) then fill the rest of the jar with half vinegar, half water.
Keep the lid on and allow to soak for at least two weeks. The liquid should look like the jar on the left, below.
The jar on the right is a copper liquor, made in the same way with copper scraps, but I found the copper scraps I used needed a few more months to turn into a nice crusty neon blue.
ABOUT IRON: This process extracts iron, or ferrous sulphate, from the rusty metal into the solution. Iron saddens the colors, which in some case is great if you'd like deeper shades, but your bright red will probably become more of a deep mauve, and a shining yellow a dusty olive. This is why it is also important to either wash tools well after using with iron, or keep a separate set of tools to use with iron like I do.
Iron reacts most strongly to dyes from plants with lots of tannins. So if you dye with say, lac which is a dye made from the secretions of a bug and does not contain much tannin, the iron will have little effect. But of you dye with black walnut, oak galls, pomegranate rinds, or myrobalan, even though these dyes can be pale on their own, since they are rich with tannin the iron will give you deep, dark charcoal greys and browns.
All that to say, each dye has its own reaction to iron, and just like anything in nature can be totally unpredictable! FUN right??
CAUTION: Iron can be damaging to some fibers. While you can use it quite freely with cotton; the silk, wool fabrics, or other animal fibers are easily damaged by iron. This might not be immediately apparent, but over the years the fabric may deteriorate more quickly.
For example, the image below is a scrap from an ornately embroidered silk jacket, looks like late 19th century, that was clearly dyed with too much iron and has almost completely deteriorated. It’s teal lining fabric, which does not look like a color dyed with iron, is still totally intact.
It is a good idea to limit iron use to just a little bit on silks and wool, and use cold water.
** (I HIGHLY recommend using different tools for iron, I have a dedicated pot, spoon, and mixing cup that I use only with iron and no other dyes or fabrics go into it. For small pieces, to-go containers can be perfect for this, or old plastic paint buckets since you wont be needing heat. Also be sure you aren’t splashing it near any other fabrics or dyes. Iron spots generally only show up on fabric after dyeing, and it is incredibly disappointing to find weird dark spots on your fabrics after spending much time and effort dyeing them.) **
Below is a page from my dye notebook with some iron tests. Each test goes like this: fabric is pre-mordanted with alum and dyed, then cut into three pieces. One piece goes directly in the book (the fabric in the middle, just an alum mordant) The fabric to the left has been post-mordanted with iron. The fabric on the right has been post- mordanted with copper. These tests are not for exact color matches, but to give you an idea of what iron will do to the dyes.
After the rusty metal has soaked in the vinegar / water mixture for a few weeks and has turned a nice dark color with rusty scum, You’ll want to strain out the liquid into your iron dyepot / bucket that is filled with just enough water to move fabric around.
It’s best to do this with gloves on as the iron can be hard on the skin and turn your cuticles dark colors. Strain using cheesecloth or a metal mesh strainer (again! only use tools that you will not use with food or with other dyes! I usually use a scrap piece of loosely woven fabric).
Start with just a few tablespoons or so of the iron liquor, depending on the size of the fabric being dyed. Much like salting a meal, you can add more later, but you can’t reverse the darkening of the iron, so a little at a time is best. After pouring this into your dyepot / bucket, mix liquids thoroughly, then add your PRE-WETTED fabric. Keep an eye on how the color is changing, and turn fabric frequently to be sure iron is getting in all parts of the fabric. Remember wet fabric is many shades darker than light fabric.
You can remove from the dyebath as soon as it reaches the shade you like. Sometimes this happens in a matter of seconds. If after 15-30 minutes of frequent spinning in the dyebath you still want a darker, more grey color, pull fabric out and add more iron liquor to the pot a few tablespoons at a time, stir to combine liquids, and add fabric back to pot.
When you’ve got the color down, rinse fabric really well so you don’t end up unintentionally transferring iron on to any other fabrics (careful not to splash on fabrics nearby!!). You can add more water and vinegar to the jar to extract more iron!
Care for these like you would any other naturally dyed fabric - wash gently and infrequently, keep out of direct sunlight, and treat with love.
Shown below, Helia Top from 2017 - dyed bright copper with cutch, then overdyed with iron for deep chocolate shade.