Dyeing with Oak Bark — Tannin Brown from the Most Common European Tree

Use 200% WOF of crushed or chopped oak bark. For 100 g of wool, weigh out 200 g of bark. Collect bark from fallen branches, pruning waste, or windfall trees — never strip bark from living oaks, as this damages the tree. Both the rough outer bark and the smoother inner bark contain tannins, but the inner bark is richer. Break or chop the bark into pieces roughly 2-3 cm across to increase surface area for extraction.

Place the bark pieces in the dye pot and cover with about 5 litres of cold water. Let them soak overnight (8-12 hours). The long cold soak begins drawing out the tannins gently — the water will turn a pale amber-brown during soaking. This pre-extraction step produces a significantly richer dye bath than heating bark directly from dry.

Bring the pot to a gentle simmer (80-90°C) and hold for 90 minutes. Oak bark releases its tannins slowly — the long simmer is essential for a full extraction. Stir occasionally. The liquid will deepen to a rich amber-brown, darker than tea but lighter than coffee. After simmering, the bark pieces will be soft and pale, having surrendered most of their colour.

Strain the dye liquor through a fine mesh strainer into a clean pot. Squeeze the spent bark to extract the last colour. The strained dye bath should be a clear, warm amber-brown. Bark fragments left in contact with the wool during dyeing can cause dark spots and uneven colour, so strain thoroughly. The spent bark can be composted or saved for a weaker second extraction.

Pre-wet the alum-mordanted wool in warm water, squeeze out excess, and lower it into the strained dye bath at room temperature. Slowly raise the temperature to 85°C over 30 minutes, then hold for 45 minutes. Turn the wool gently every 10 minutes for even colour uptake. Oak tannins bond to wool even without mordant (they are substantive), but alum-mordanted wool produces warmer, more golden-brown tones compared to the cooler grey-brown of unmordanted wool.

Turn off the heat, cover the pot, and let the wool cool in the dye bath overnight. The slow cooling allows the tannins to continue bonding, deepening the final colour. Remove the wool the next day, squeeze gently, and rinse in lukewarm water until the runoff is mostly clear. The final colour on alum-mordanted wool is a warm golden-tan to medium brown — the colour of old leather, of autumn leaves, of the forest floor. An iron afterbath shifts the colour to deep grey. Oak bark dye has good washfastness and moderate lightfastness — it fades slowly in direct sunlight but holds well indoors.