A mordant is a substance that helps ‘dyeing stuff’ bond to fibres. Mordants are often a metallic salt, but they are also non-metallic substances, such as Tannin and Oxalic Acid that also act as a chemical bridge between the dye and the fabric . Urine, blood, manure, soymilk, rhubarb leaves and persimmons are some examples of some of these non-metallic mordants that have been used traditionally, for different fibres, contexts, and locations across history and many civilisations.

A few but important number of natural pigments and dyes that are substantive, i.e. do not require the use of a mordant to be light- or wash-fast. When using those, such as Indigo, Eucalyptus or Madder you can skip this process. Many dyes, even if substantive, do benefit from using a mordant to intensify or change the final colour.


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. Sometimes I choose to use no extra heat but leave fibres in the mordant bath for 4 or 5 days instead; ensuring I give them a stir a couple of times a day.
  • Mordants are to be used in the same proportion. You can add less to get a paler shade but do not add more as it is likely to damage the fibres.
  • Wet fibres beforehand for at least 5 minutes, or until they are thoroughly wetted, 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, yet, 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 (link to Dyeing page under page Recources).
  • 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. I use my baths several times, sometimes without adding anymore, taking the opportunity to do some experimenting and testing alongside.
  • Mordanting can also be used as a design feature in your colour making adventures. There is a lot to learn from traditional knowledge from Asian heritage (link to Dyeing page under Resources)

Mordanting Different Fibers

  • 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 hot water first to at least 82° 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 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. There is a lot to learn and find out here too. For instance, the tannins from the Persimmon tree are quite special and unique.

Tannins Family

Most Tannins will add some colour to your fibres so consider that when planning for your end colour.

Gallic tannins: Clear tannins that do not add much colour to the fabric.

  • Tara pods
  • Oak galls
  • Oak bark
  • Sumac (leaves, 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 stale urine around – despite the clear financial benefit of this ingredient.

I only use those I know I can safely manage, including its careful disposal. I use traditional mordants like Iron (Ferrous Sulphate), Copper (Copper Sulphate), Oxalic Acid, Alum, and Aluminium Acetate. Wear Gloves and facemask when handling, and make sure the area is well-ventilated when heating- not a problem in my new garden studio.

In the business of dyeing, one must remain watchful of practices and safety, it can be far from simple. Remember for instance, that Rhubarb leaves are full of Oxalic Acid, quite toxic and NOT to be eaten – only the lovely tangy stalks that you can cook afterwards, plenty of delicious recipes for that.

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, Turkey Red Journal, has this year 2020 celebrated their 25th anniversary. Their article on mordanting cotton gives a excellent overview of how methodical exploration and experimentation 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.