Why preparation decides your result

Natural dyes are generous, but they are not forgiving of a grubby cloth. A new length of cotton arrives coated in sizing, spinning oils and mill finishes; a fleece carries lanolin and dust; even a charity-shop linen sheet holds years of fabric conditioner. Dye cannot grip what it cannot touch, so a poorly prepared piece gives you pale, patchy colour that bleeds away in the first wash. Good preparation, by contrast, gives you depth, clarity and a colour that survives years of use. There are three stages to work through — scouring, tannin and mordanting — and each takes an afternoon rather than an hour.

Scouring: removing the invisible barrier

Scouring is simply a deep, purposeful wash. Its job is to strip away anything sitting between the fibre and your dye pot. Weigh your fibre dry first; every quantity from here on is measured as a percentage of that dry weight, which dyers call WOF — weight of fibre.

• Cellulose (cotton, linen, hemp, nettle): simmer for 60–90 minutes in soft water with 2–5% WOF washing soda and a small squirt of pH-neutral detergent. Cotton and linen are robust; they can take a gentle rolling boil without complaint.
• Protein (wool, silk, alpaca): treat these far more kindly. Use 1–2% WOF pH-neutral soap flakes or a mild washing-up liquid and hold the bath at 55–60°C for 30–45 minutes. Never boil, never agitate, and never move wool between hot and cold water quickly — that is how felt happens.
• Already-loved textiles: old sheets, shirts and blankets are excellent candidates, but they hold residues. Give them a longer scour and rinse until the water runs completely clear.

Rinse thoroughly in water of a matching temperature. If the fibre still smells of soap or feels slick, rinse again. Nothing you do later will compensate for a half-scoured cloth.

Tannin and mordant: giving colour something to hold

Most natural dyes are not chemically attracted to fibre on their own; they need a bridge. On protein fibres, alum forms that bridge directly. On cellulose, the bond is weaker, so plant fibres benefit from a tannin pre-treatment first.

Tannin bath: simmer scoured cellulose for 45–60 minutes with 5–10% WOF of a tannin source — oak gall, sumac, myrobalan or even strong black tea. Tannins add a warm undertone, so keep that in mind for pale blues and greens. Let the fibre cool in the bath, then rinse lightly.

Alum mordant: use 10–15% WOF alum for cellulose and 8–10% WOF for wool and silk. Wool also likes 6% WOF cream of tartar, which brightens colours and softens the hand of the yarn. Dissolve the powders fully in a little hot water before adding them to the pot.

• Cellulose: bring the bath to 80–85°C, hold for 45–60 minutes, then cool overnight in the liquid.
• Protein: hold at 80°C for 45 minutes, then let the pot cool slowly with the fibre still inside.

Cooling in the bath matters more than most beginners expect. It lets the mordant penetrate evenly instead of sitting on the surface, and it protects wool from the shock of sudden temperature change.

Water, pots and temperatures

Use soft water wherever you can. Rainwater, filtered water or a kettle-descaled supply gives noticeably clearer, brighter colour than hard tap water, whose minerals dull dyes and can leave chalky deposits. If your water is stubbornly hard, a pinch of citric acid or a little distilled water in the bath will help.

For equipment, choose stainless steel or enamelled pans large enough that the fibre moves freely. Avoid aluminium, which reacts with tannins and leaves dull, greyish results, and avoid unlined iron unless a deliberate saddening effect is what you want. Keep dye pots separate from kitchenware, and reserve a long wooden spoon and a pair of tongs for dyeing alone.

Rinsing, testing and storing

Once mordanted, rinse the fibre in warm water until it runs clear, then either dye it straight away while damp or dry it thoroughly for later. Damp fibre takes up dye most evenly, so if you can move directly from mordant bath to dye pot, do.

Before committing a whole piece, cut a small swatch and test it. It costs you half an hour and saves a garment. Keep a notebook of weights, percentages, temperatures and timings — a natural dye recipe is only repeatable if you wrote it down. Store prepared, dried fibre in a cotton bag or paper wrapper, away from damp and direct sunlight, and label it with the date and mordant used.

Patience as part of the palette

Slow textiles reward the unglamorous stages. Scouring, tannin and mordanting are not the photogenic part of natural dyeing — there is no dramatic colour shift, no alchemy in the pot — yet they are the reason a naturally dyed cushion cover still looks rich after three winters of washing and sunlight. Give your cloth the time it needs before the dye goes in, and the colour you pull out at the end will hold its ground beautifully.