A mordant is a substance that helps ‘dyeing stuff’ bond to fibres. It forms a chemical bridge between the dye and the fabric . Mordants are often a metallic salt, but they are also non-metallic substances, such as Tannin or Oxalic Acid . Urine, blood, manure, soy milk, rhubarb leaves and persimmons are also examples of traditional non-metallic mordants. These have been used for different fibres, contexts, and locations across history and many civilisations.
A few but important natural dyes are substantive, i.e. do not require the use of a mordant to be light- or wash-fast). When using those, you can skip the mordanting process. Many dyes, even if substantive, do benefit from using a mordant to intensify or change the final colour, like Rubia Tinctoria.
Mordanting chart guide
General considerations using mordants
There are lots of considerations to bear in mind when using mordants, here are some of my findings:
Time, Temperature and Concentration are the main players in this chemical reaction. For instance, a higher temperature or concentration of dyestuff will need less time for dyeing. When leaving fibres in the mordant bath make sure to give them a stir a couple of times.
Mordants are to be used in the same proportion. You can add less to get a paler shade, but adding more can easily damage the fibres.
Wet fibres beforehand for at least 5 minutes, especially if tightly woven fabric. Allow at least an hour for wool; some would even say that an overnight soak is best. Wool fibres are water repellent to start with. However, once wet, they hold on to the water equally strongly and need longer drying time than other fibres.
Use a ratio of about 3 litres of water to 100g of fibre.
You can dry and store these fibres for a couple of months or dye them straight away.
Mordant baths can be replenished and kept going for a while, there seems to be a rule of thumb of adding half the amount of what you added to the first bath. Using baths several times without replenishing the mordant offers the opportunity to do some experimenting alongside.
Mordanting can also be used as a design feature in your colour making adventures. There is a lot of traditional knowledge from the Asian and African continents.
Mordanting different fibres
- Please refer to the Mordanting Chart show above for specific instructions on mordanting different fibres.
- Potassium Aluminium Sulphate, also known as Alum, needs to be dissolved in warm water, in between 40° to 60° before adding all the water and stir, then placing the fibres.
- When mordanting vegetable fibres rinse thoroughly and soak well in Calcium Carbonate or Wheat Bran for a few minutes in warm water and then a thorough rinse before leaving to dry or begin the dyeing process.
Tannins
Tannins are an excellent match for vegetable fibres, they bond well with cotton and linens, with or without Aluminium Acetate. I think this is one of those areas where there are as many as possible recipes as there are cooks.
A large number of Tannins can be found in tree barks, seeds, peels and fruits. They great sources of greys and blacks, as well as other antibacterial and protective properties. For instance, the tannins found in the Persimmon tree are quite special and unique. Here you will find a post just on Tannins.
Most Tannins will add some colour to your fibres so consider that when planning for your end colour. Here is a list of traditional sources of tannins:
Gallic tannins: Clear tannins that do not add much colour to the fabric.
- Tara pods
- Oak galls
- Oak bark
- Sumac (leaves and galls)
Ellagic tannins: Tannins with a lot of flavonoids that will add a yellow colour to the fabric.
- Myrobalan
- Pomegranate
- Henna
Catechic tannins: Condensed tannins that will add brown and reddish hues to the fabric.
- Black tea
- Cutch
- Quebracho
- Chestnut bark
Safety considerations when using mordants
Some of these usages are not safe and it is important to be mindful, for your own health, and that of others. For instance I do not use the likes of Tin (Stannous Chloride) or Titanium Oxalate ⚠. For completely different reasons, I dislike the idea of using stale urine – despite being so clearly available.
The use of traditional mordants like Iron (Ferrous Sulphate), Copper (Copper Sulphate), Oxalic Acid, Alum, and Aluminium Acetate is quite safe. I do not always remember to wear gloves and face mask when handling, but, make sure you work in a well-ventilated area when heating mordants.
In the business of natural dyeing, be watchful of practices and safety . For instance, the Rhubarb leaves are full of Oxalic Acid ⚠, a great mordant for cotton but quite toxic if eaten – only the lovely tangy stalks that you can cook afterwards, plenty of delicious recipes for that. Peach leaves and bark have lovely colours and make lovely eco prints, but as they wilt they are full of cyanide ⚠.
Once you feel you are ready to dispose of it, make sure you water them down as much as you can to dilute the mix and water your plants and garden – or mindfully dispose of it.
Further resources on mordanting
You can find more information and different approaches to mordant fibres in my resources pages, but here are some quite specific to mordanting:
- Great set of instructions on how to mordant your fibres on Botanical Colours, a great website to explore and learn more about natural dyes.
- A journal dedicated to natural dyes, Red Turkey Journal has in this year 2020 celebrated their 25th anniversary. Their article on mordanting cotton gives an excellent overview of how methodical exploration can help us learn and develop the art and science of nature dyes.
- Rebecca Desnos for instance uses soya bean milk and tannins solely when preparing her fibres, her website is worth a visit.
