Cream of tartar
Cream of tartar (potassium bitartrate) is a salt of tartaric acid. It is commonly obtained as a sediment produced in the wine-making process. Cream of tartar is an optional addition to the dyebath to soften wool, brighten shades, and point the colour of some dyes (it will move the fuschia of cochineal to a pure red). Cream of tartar works best with protein fibres but is seldom used with silk. It is not used with cellulose fibres. Use at 5-6% WOF.

Iron – Ferrous sulphate
Like alum, Iron is a metal mordant which will increase the fastness of any colour. Unlike alum however, It is far from neutral; making other dyes darker and richer. Iron will also "sadden" bright colours. It is most often used with cellulose fibres like cotton, linen, rayon and hemp and should be used with care on protein fibres as it can make them slightly hard or brittle. If used in the mordant process colour shifts are more distinct than if added while dyeing. Most dyers apply iron as a post-dye process. Iron should be used at 2-4% WOF. Above 4% may damage fibres.

  1. Measure ferrous sulphate at 2% WOF. Dissolve in hot water. Add to kettle. Fill the kettle with enough hot water to fully cover the fibre when added.

  2. Add wet, mordanted or dyed fibre,

  3. Heat to 71 - 77ºC (160 - 170ºF) hold for 30 minutes.

  4. Rinse well. Remember to thoroughly scrub a pot that has been used to iron mordant or it will contaminate the next dye.

Homemade Ferrous Acetate

When printing with natural dyes, we recommend changing ferrous sulphate to ferrous acetate to avoid bleeding and ferrous transfer (the migration of iron).

  • 5 g ferrous sulfate

  • 100 ml vinegar

  • 3 g lime (calcium hydroxide) 

Combine the below ingredients in a plastic container and stir well. If thickening is required, weigh the amount of ferrous acetate you wish to thicken and add 1% of guar gum.

Ferrous acetate needs to be fixed to the cloth. We use chalk (calcium carbonate) 50g in 5 litres of warm water. Once your goods that have been treated with ferrous acetate are fully dry, dip them into this solution. This solution may be kept and reused again and again. Generally you may refresh with 50 g of chalk after each 10 kg of fabric.