Dyeing Yellow with Dyer's Broom — The Greenweed That Made Lincoln Green

Use 100% WOF of dried flowering tops — flowers, leaves, and young stems. For 100 g of wool, weigh out 100 g of dried plant material. Harvest dyer's broom when the small yellow pea-like flowers are fully open, typically in June-July. Cut the top 20-30 cm of stems. Dry loosely bundled in shade for 1-2 weeks until brittle. The dried plant retains a faint green colour and mild herbal scent.

Place the dried dyer's broom in a dye pot with 4 litres of warm water and soak for at least one hour. The water will turn a pale golden-green as the flavonoids begin to dissolve. The woody stems take longer to hydrate than the flowers and leaves. Pressing the material below the surface ensures even extraction.

Bring the pot to a gentle simmer (75-80°C) and hold for 40 minutes. Do not boil — excessive heat dulls the yellow. Stir occasionally. The liquid will deepen to a warm golden-yellow. The flowers will lose their colour and the stems will darken as the pigment transfers to the water.

Strain the dye liquor through a fine mesh strainer into a clean pot. Press the spent plant material to extract all remaining yellow liquid. The strained liquor should be a clear, warm golden-yellow.

Pre-wet the alum-mordanted wool in lukewarm water for 15 minutes, squeeze gently, and lower it into the dyer's broom bath at room temperature. Slowly raise to 80°C over 15 minutes, then hold for 45 minutes. Turn gently every 10 minutes. The wool will develop a warm, clear golden-yellow — the colour that medieval English dyers over-dyed with woad to create Lincoln green.

Turn off the heat and let the wool cool in the dye bath overnight. Remove, squeeze gently, and rinse in lukewarm water until the runoff is clear. The final colour is a warm golden-yellow, slightly warmer and less green-tinted than weld. Lightfastness is moderate to good. Dry in shade.