Alum is particularly effective when used as a fixing agent for natural dyes and plant colours in botanical eco-printing. Alum mordant acts as a bridge between dye and fibres and helps to brighten colours. It links chemically with the fibre and creates attachment points which bond with the colourant from natural dyes creating light and wash fast colours. Alum Synonyms: Potash Alum, Aluminium Potassium Sulphate, Aluminium Potassium Sulfate.
Some natural dyes will colour protein fibres such as wool and silk without an assistant but most will require a mordant to ensure the colours are washfast. Alum mordant is the most widely used mordant for dyeing with natural dyestuff. Cellulose fibres, which include cotton, linen and viscose require a combination of Alum and a tannin to make the colours permanent, or they can be mordanted using Aluminium Lactate.
Natural Dyeing – using Alum as a mordant for silk and wool:
- Soak materials in warm water and squeeze out excess before adding to the mordant bath.
- For every 250g of the dry wool or silk, use 50g of alum mordant in 5 litres of water. Add 10g of Cream of Tartar to help soften the fibre and further brighten the colours.
- Gradually heat the mordant bath to around 80°C for 30 minutes and allow to cool slowly.
- Remove the materials and squeeze to remove excess liquor. Do not rinse.
- After mordanting, the materials can be simmered with any of the natural dyes. Place the dyestuff in a mesh bag before adding to the dyebath.
- Simmer for approximately 30 minutes and turn off the heat. Allow the material to cool slowly in the dyebath before removing it.
- Gently rinse out excess dye in clean water.
The process of mordanting cotton, linen and other cellulose fibre for natural dyeing is different in that the mordants do not stick to the fibre. The cellulose fibre needs first to be soaked in a solution of tannin so that a mordant can attach itself to the tannin.Â
Alum is used to treat fabrics and paper prior to marbling to help paint transfer. It helps to treat fabrics and paper in a solution of Alum prior to using marbling paints as this will help the colours to transfer more clearly. Dissolve 10g of Alum in 4 litres of warm water. Sponge or spray the Alum solution onto paper and allow to dry before marbling. Fabrics need to be fully wetted in the Alum solution, wrung out and allowed to dry without rinsing. The dried fabric can be safely ironed to ensure a wrinkle free surface for the marbling paint.
Alum mordant has also become popular for use in Botanical Printing, also known as ECO printing. This experimental technique is effective on cotton and linen fabrics (the cellulose fibre needs first to be soaked in a solution of tannin so that the alum can attach itself to the tannin), as well as wool fabrics including felt, silk fabric and cotton paper. The material is first soaked in a 10% solution of alum mordant (100g to 1 litre) or alum and iron solution and leaves and petals are placed onto it while it is still damp. The fabric is folded, rolled up and parcelled in cling film or aluminium foil before being steamed to extract the colour. Likewise, leaves and petals can be sandwiched between sheets of mordanted paper and steamed. See here for our steaming instructions which are used to heat-set silk dyes and can also be used for Botanical Printing.
Please note that there are hazards associated with the use of this product. Follow the advice on the label at all times.Â
