Dyeing Wool with Willow Bark and Leaves

Willow is one of the most generous trees in the British landscape. It grows quickly, coppices hard, and gives basket makers an endless supply of rods — but the bark and leaves hold something else too: soft, gentle browns that sit beautifully on wool. If you have ever admired the muted fawn of an old willow basket, you already know the colour. What follows is a practical route to getting it onto fleece, yarn or knitted fabric at home, using nothing more exotic than a large pan, a mordant and a bit of patience.

Why Willow Gives Such Gentle Colour

Willow bark is rich in tannins, and it is the tannins that do most of the work. They bond readily with protein fibres such as wool, which means willow dyes are forgiving — you rarely get a harsh or patchy result. The trade-off is that the colours are quiet: buff, oatmeal, pale fawn and, with a little help, a deeper russet-brown. Treat willow as a dye for subtlety rather than drama. It layers beautifully under or over other natural dyes and gives a wool that looks as though it has simply grown that colour.

Different willows behave differently. Crack willow and white willow give the warmest browns from bark, while goat willow, or sallow, tends to be softer and slightly greener. Osier and the basketry willows are perfectly usable too. If you are lucky enough to have several to hand, dye small skeins from each and keep a note of which tree gave what — it is the only reliable way to learn your own patch.

Harvesting Willow With Care

• Bark: the traditional time is spring, when sap is rising and bark peels easily from coppiced rods. If you are working with a basket maker's prunings, peel the rods before they dry. Never ring-bark a standing tree — it will kill it.
• Leaves: pick in late spring and early summer, when they are fully open but still fresh. Leaves give a lighter, more golden tan than bark and are the better choice if you would rather not remove bark at all.
• Quantity: roughly equal weights of fresh bark to dry wool is a good starting point. For dried bark, halve it. With leaves, aim for a loosely packed basketful for every 100g of wool.
• Dry it: spread bark and leaves somewhere airy and out of direct sun. Once dry, they keep for a year or more in paper sacks.

Preparing Your Wool

Natural dyes need clean fibre. Scour your wool first in warm water with a little soda ash or a pH-neutral wool wash — around 40 to 50°C for twenty minutes is plenty — then rinse gently. Never shock wool with sudden temperature changes, or you will felt it before you have dyed it.

Next, mordant. Alum gives the clearest, most predictable browns on willow. For 100g of dry wool, use about 10g of alum and 8g of cream of tartar. Dissolve both in hot water, top up the pan so the wool can move freely, add the wetted wool, and heat slowly to about 80°C. Hold it there for an hour, then let the whole pan cool overnight. Squeeze the wool rather than wringing it. Mordanted wool can be dried and stored for weeks before dyeing, which makes it easy to spread the work over several days.

Making a Bark Dye Bath

Soak your dried bark overnight in enough rainwater to cover it generously — rainwater is worth using if your tap water is hard, as lime can dull the colour. The next day, bring the pan slowly up to a gentle simmer and hold it just below boiling for an hour to ninety minutes. Strain the liquor into your dye pan and discard the spent bark.

Add the mordanted wool, bring the bath slowly to 80 to 90°C, and hold it there for an hour. Stir only occasionally and gently. Then turn off the heat and leave the wool in the cooling bath overnight. The colour will deepen as it cools. Expect a soft beige from a single bath; two or three successive baths, using the same wool in fresh liquor, build a respectable mid-brown.

Dyeing With Willow Leaves

Leaves are quicker and lighter work. Simmer them for about forty-five minutes, strain, and dye exactly as with bark, though you can afford a slightly shorter dyeing time of forty minutes. The result is a paler, more golden tan with a faint green edge to it — lovely on its own for laceweight or for wool destined for Fair Isle knitting, where it sits well beside indigo and madder.

Shifting the Shade

A few simple modifiers transform willow browns.

• Iron: a pinch of ferrous sulphate in a separate bath, dipped for ten to twenty minutes, turns the wool a cool grey-brown or sage. Go sparingly — iron can make wool brittle.
• Copper: gives a deeper, greener brown, and slightly improves lightfastness.
• Alkaline: a little soda ash or wood-ash water deepens and warms the tone towards russet.
• Acid: a splash of vinegar brightens and clarifies the tan.

Keep dedicated pans and spoons for dyeing, wear gloves, and work somewhere well ventilated. Willow dyes are only moderately lightfast, so store finished pieces away from strong sunlight. Labelled sample skeins, kept in a drawer with the date and the tree noted, will teach you more than any book — and within a season you will have a small palette of honest, home-grown browns that no synthetic dye quite matches.