Preparing Fabric and Yarn for Natural Dyeing

Why Good Prep Makes or Breaks a Natural Dye

There is nothing quite like lifting a skein of wool from a pot of simmering nettle or madder and watching the colour bloom. But the truth is that most disappointing natural dye results are not caused by the dye plants at all. They come from fibres that were never properly scoured, or a mordant that was rushed. Spend the time at this stage and your colours will be deeper, more even, and far more resistant to sunlight and washing.

Natural dyes sit on the surface of a fibre rather than soaking into it the way synthetic dyes do. Oils, waxes, pectins and manufacturing finishes block that surface, and without a mordant there is nothing to anchor the pigment. The good news is that preparation is simple, cheap, and mostly a matter of patience rather than equipment.

Scouring Plant Fibres: Cotton, Linen and Hemp

Cellulose fibres arrive with a natural waxy coating and often a sizing applied by the mill. Both need removing. You will need a stainless steel or enamel pan, washing soda (soda ash), and a pH-neutral washing-up liquid. Work out your fibre's dry weight first, because everything from here on is measured as a percentage of that weight — known as WOF, or weight of fibre.

• Use 2–5% WOF washing soda plus a small squirt of washing-up liquid in enough water to let the fibre move freely.
• Add the fibre to a lukewarm bath, then raise the heat slowly to 80–90°C and hold for an hour, stirring gently every ten minutes.
• Let it cool in the bath, then rinse in water of a similar temperature until it runs clear.

When cotton is properly scoured, water sheets off it rather than beading. If it still feels waxy, repeat the process. Linen and hemp can take a full boil without harm. Do not use biological detergent — the enzymes can damage the fibre and leave residues that interfere with mordanting.

Scouring Wool and Silk Without Felting

Animal fibres are far more delicate and will felt if you treat them like cotton. Alkalinity is the enemy here, so leave the washing soda in the cupboard and reach for a pH-neutral soap — a simple olive oil soap or a dedicated wool wash is ideal.

• Use 2–3% WOF soap in water at 40–50°C, no hotter than your hand can comfortably bear.
• Soak for 30–45 minutes, pressing the fibre gently under the water. Never rub, wring or agitate.
• Allow the bath to cool before lifting the fibre out, and rinse in water of the same temperature.

Silk needs an even lighter touch: 30–40°C, twenty minutes, and the mildest soap you have. Sudden temperature changes are what cause wool to shrink and mat, so always match your rinse water to the bath.

Mordanting: The Bridge Between Fibre and Dye

Alum — potassium aluminium sulphate — is the workhorse mordant for most natural dyers. It is safe to handle, gives clear, bright colours, and works on both plant and animal fibres. Cream of tartar is often added alongside it to soften wool and brighten tones.

• Wool and silk: 8% WOF alum with 6% WOF cream of tartar.
• Cotton, linen and hemp: 10–20% WOF alum. Cellulose often benefits from a tannin pre-bath first — 5–10% WOF of oak gall, sumac or gallnut — followed by the alum bath.

Dissolve the alum in a jug of hot water before adding it to the pot; undissolved crystals leave speckles. Add your pre-soaked, still-damp fibre to a lukewarm bath, raise the temperature slowly over half an hour, then hold at 80–90°C for 45–60 minutes. Turn off the heat and leave the fibre to cool overnight in the liquor. This slow cooling is where much of the bonding happens, so resist the urge to hurry it.

Use stainless steel or enamel, and keep a separate pot for mordanting and dyeing if you can. Iron and copper pans will introduce their own colour shifts — sometimes lovely, but rarely repeatable.

Rinsing, Resting and Storing

Once the mordant bath has cooled, lift the fibre out and rinse gently in water of the same temperature until the water is mostly clear. You are not trying to rinse all the mordant away, only the excess.

The best state for dyeing is damp, not dry. Squeeze wool gently rather than wringing, wrap it in a towel, and either dye it straight away or store it in a sealed bag in the fridge for a day or two. Damp fibre absorbs dye more evenly, and the resting period lets the mordant settle into the fibre. Any longer than three days and you risk mildew.

Water quality matters more than most guides admit. If you garden in a hard water area, calcium can dull your colours and leave a chalky bloom on dark shades. Rainwater from a butt is ideal, and it costs nothing to collect a few litres before a dye session.

Small Habits That Pay Off

• Weigh every fibre dry, before scouring, and write it down. All your percentages depend on it.
• Keep a notebook: fibre, WOF, temperatures, timings, water source, and the result. Two seasons from now it will be your most valuable tool.
• Never mordant wool and cotton in the same bath — they need different conditions and different quantities.
• Test with a small skein before committing a whole fleece or a metre of precious linen.

Do this groundwork well and the reward is a store cupboard of yarn and cloth ready for whatever the garden gives you — whether that is onion skins saved through winter, marigolds from the cutting bed, or a bundle of willow bark stripped on a damp afternoon.