Natural dyeing is a slow, rewarding craft, but the colour you achieve depends as much on preparation as on the dye plants themselves. For small studios, where every batch matters, taking time to scour and mordant fabric properly is the difference between a rich, lasting hue and a disappointing wash of colour. This guide walks you through simple preparation steps for cotton, linen, and wool.

Why Preparation Makes or Breaks Your Dye

Every fibre arrives with a coating that blocks dye. Cotton and linen carry natural waxes, pectins, and sizing from weaving. Wool and silk hold lanolin, sericin, and spinning oils. If you dye without removing these, the colour sits on the surface and rinses away. Scouring removes the barriers. Mordanting then creates a chemical bridge between the fibre and the dye molecule. Without a mordant, many plant dyes — madder, weld, onion skins — simply will not bind. For small studios, consistency is everything. Weigh your fibre dry, use soft water where possible, and keep notes on every step.

Scouring Cotton and Linen

Plant fibres are robust and can take a good hot scour. For 100g of dry fabric, you will need about 5g of washing soda (sodium carbonate), 2g of pH-neutral soap, and 4 litres of water. Dissolve the soda and soap in hot water, then add your pre-wetted fabric. Bring the bath to 80–90°C and hold it there for one hour, stirring gently every 15 minutes. Do not let it boil vigorously, as this can weaken the fibres. After an hour, drain and rinse in warm water until it runs clear. If your linen still feels stiff or waxy, repeat the process. Well-scoured cotton will absorb water instantly and feel almost rough — that is exactly what you want.

Scouring Wool and Silk Gently

Protein fibres need a far gentler approach. Sudden temperature changes or alkaline conditions will felt wool or dull silk. Use 1g of pH-neutral soap per litre of soft water at 30–40°C. Soak your wool for 30–45 minutes without agitating. Never rub or wring wool — just let it soak. Rinse in water of the same temperature. For silk, you can go up to 40–50°C, but still avoid any friction. If your silk is raw and still contains sericin, a slightly longer soak with a little more soap will remove it. After scouring, wool should feel clean but still have its natural lanolin softness. Silk will feel soft and supple.

Mordanting with Alum for Even Colour

Alum (potassium aluminium sulphate) is the safest and most reliable mordant for home studios. Use 10–15% weight of fibre (WOF) for cotton and linen, and 5–8% WOF for wool and silk. Add 1–2% cream of tartar to brighten colours and prevent them turning dull. Dissolve the alum in a little hot water, then add it to enough water to cover your fibre. Add your pre-wetted, scoured fibre. For cellulose, heat to 80–85°C and hold for one hour. For wool, keep it at 60–70°C for one hour. Let the fibre cool in the bath overnight — this improves uptake. Rinse lightly before dyeing.

Tannins and Pre-Treatments for Cellulose

Cellulose fibres often benefit from a tannin pre-treatment before alum. Tannins act as a bridge, helping the mordant attach. You can make a tannin bath from oak galls, pomegranate rind, or even strong black tea. Use 5–10% WOF of tannin material, simmer for one hour, then let the fibre cool in the liquid. After that, proceed with alum mordanting. For a gentler alternative, soak scoured cellulose in a mixture of one part soy milk to four parts water for 12–24 hours. Hang to dry without rinsing, then mordant. Soy milk gives softer, slightly muted colours that suit slow stitching and hand-sewn projects.

Rinsing, Drying, and Testing Your Results

After mordanting, rinse your fibre in cool water until the water runs clear. Do not use detergent at this stage. Dry in the shade to avoid UV damage. Before you dye a full batch, always test a small sample. Keep a dye journal: record fibre weight, mordant percentage, water pH, temperature, and time. Hard water can cause dull colours, so use filtered or rainwater if you can. After dyeing, wash your fabric with pH-neutral soap and dry in the shade. Proper preparation means your hand-sewn cushions, garments, and quilts will hold their colour for years, not months.