Mordants and Fixatives

Info about Mordants 

To be successful at natural dyeing you need to know a bit about mordants and fixatives. Basically natural dyes will not adhere to natural fibres without the use of a mordant or fixative and while you may initially get a beautiful result from your natural dyeing it will soon wash out or fade away. Protein fibres like silk and wool need a plant extract (Dye) and a mineral mordant, so if you are looking to dye some yarn to eventually produce a garment that will wash well you need to know a little about mordants.

Soaking the wool or yarn in water to which a mordant has been added will ensure your lovely natural dye fixes to what you are dyeing.  To do this fill your pot with cool water to which your mordant has been added. Stir well to ensure the mineral has dispersed through the water evenly and then place your dye material (wool, fibre, yarn, thread) gently into your pot. Slowly bring to a simmer for about 20 to 30 minutes and then turn the heat off and leave to cool.  Basically as the water cools the mordant will adhere to the fibre or yarn in the pot. At this stage you can dry your mordanted yarn and store it for later use or transfer to your dye bath where the natural dye color you have chosen will fix itself to the mordant in your yarn or fibre.

Natural Dyeing – Mordants

  • Alum – The specific compound is the hydrated potassium aluminium sulfate . Alum can sometimes be found in your local supermarket as it is often used in canning and preserving.  Alum is one of the most popular mordants used in natural dyeing as you can dye and mordant all at the same time.  Just add your Alum to your dye bath and mix well then add yarn or fibre. Note: too much Alum can make your yarn sticky so less is best, however you may need to experiment to get a deeper color.  A good starting point is 1/4lb Alum and 1 oz Cream of Tartar to 1lb wool or yarn.
  • Iron– or Ferrous Sulphate tends to darken the dye on your fibre or yarn.  Use to create lovely browns. 1/2 oz (15 grams) Iron per pound (500 grams) fibre. Old nails boiled in water will also create an iron mordant.  Iron will dull down colors so care must be taken if that is not the look you were going for.

    Image Credit a.adrian on Flickr

  • Copper – Old pennies are made of copper and can be used as a mordant however it is more effective to buy copper sulfate to use in natural dyeing.  Copper produces lovely greens.  The measurements are the same as for iron. Copper is toxic, please see warning notes below.
  • Tin – As a mordant has a tendency to be very harsh on the wool or yarn and can make it quite brittle so small amounts are recommended.  However, when used correctly tin leaves a clear and very fast color.  Because of the harshness of tin it is most often used in tiny amounts along with another mordant or is added as an after bath to brighten colors. Tin is highly toxic, please see warning notes below.
  • Chrome – Use at a rate of 2 – 4% Chrome to wool weight. The advantage of using chrome is that it leaves the wool soft to the touch, whereas the other mordants can be quite harsh leaving your wool slightly crunchy.  Chrome is highly toxic, please see warning notes below.


Cottons and linens or other plant based textiles need a fixative to help set the dye so that your wonderful creation does not lose color quickly.

  • Salt – Use salt as a fixative for cotton fabrics, thread or yarns.  As a general rule you should use 1 part salt to 16 parts water.  Place your dyeing medium into the salted water and simmer for about an hour to allow maximum absorption.  Gently squeeze the salted water from your dyeing medium and then while still wet immerse the item into the dye bath.
  • Tannins – Tannins occur naturally in some plants which eliminate the need for other fixatives.  These plants are indicated by ** in the colors page on this site.
  • Vinegar – 1 part vinegar to 4 parts water.  Use as per salt above.
  • Baking Soda – 1/2 cup baking soda to 1 gallon water, Simmer.
  • Tara Powder 
  • Cream of Tartar – Cream of Tartar is often used with Alum mordant to produce a clearer color in the final dyed product
  • Washing Soda

Caution: Some dyes and mordants are poisonous. The use of Copper, Tin and Chrome mordants has decreased over recent years as dyers become more environmentally aware and health conscious.  

Be safe and follow some simple rules:

  • Never use the same pots and utensils for dyeing that you use for cooking.
  • Wear rubber gloves and use a face mask when measuring mordants and dyes.
  • Work in a well ventilated area.
  • Dispose of used mordants and dye baths safely.