Dyeing Yellow-Orange with Rhubarb Root — The Anthraquinone Dye of Central Asia

Use 100% WOF of dried rhubarb root. For 100 g of wool, weigh out 100 g of dried root. Dried rhubarb root is sold as sliced or chopped pieces — yellow-brown on the outside, deep yellow to orange inside. Chop any large pieces into 1-2 cm fragments to increase surface area. If starting from whole dried root, it can be very hard — soak briefly in warm water to soften before chopping. The root should have a bitter, astringent smell.

Place the chopped root in a dye pot with 4 litres of warm water and soak overnight (8-12 hours). The water will turn a deep golden-yellow to orange as the anthraquinones and flavonoids dissolve. Rhubarb root is dense and releases dye slowly — the overnight soak is important for thorough extraction. By morning, the liquid should be a rich amber-orange.

Bring the pot to a gentle simmer (80°C) and hold for 60 minutes. Stir occasionally. The liquid will deepen to an intense golden-orange. Do not boil — moderate temperatures preserve the clarity of the anthraquinone yellows. The root pieces will soften and pale as their pigment transfers to the water. A second extraction in fresh water will yield a lighter, more yellow bath.

Strain the dye liquor through a fine mesh strainer into a clean pot. Press the root pieces to extract all remaining orange-gold liquid. The strained liquor should be a deep, clear golden-orange — noticeably more orange than most flower-based yellow dyes.

Pre-wet the alum-mordanted wool in lukewarm water for 15 minutes, squeeze gently, and lower it into the rhubarb root dye bath at room temperature. Slowly raise to 80°C over 20 minutes, then hold for 45-60 minutes. Turn gently every 10 minutes. The wool will develop a warm yellow to golden-orange. The alum mordant enhances the yellow tones. Rhubarb root also contains oxalic acid which acts as a mild mordant itself, meaning the colour bonds well even to lightly mordanted wool.

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 yellow-orange — deeper and more orange than most plant yellows due to the anthraquinone content. Lightfastness is good — better than turmeric or onion skin, approaching madder. This is because anthraquinones form more stable bonds with the alum-fibre complex than flavonoids do. Dry in shade.