Dyeing Wool with Onion Skins and Madder Root

Two Storecupboard Dyes Worth Mastering

Onion skins and madder root sit at opposite ends of the dyeing tradition — one arrives free with the weekly shop, the other has been cultivated for reds since Roman times — but they behave on wool in much the same way. Both give warm, generous colour: apricot and amber from onion skins, brick reds and terracotta from madder.

What they will not do is stay put on their own. Wool needs a mordant, a metal salt that binds dye to fibre, if the colour is to survive washing and daylight. Get that step right and these two dyes will hold their ground for years.

Gathering the Dyestuff

Keep a bag in the freezer and add to it as you cook. The quantities below are enough for roughly 100g of dry wool.

• Brown and yellow onion skins: about 100g loosely packed — a well-filled carrier bag. The papery outer skins from the shop are ideal.
• Red onion skins: the same quantity, kept in a separate bag. They behave quite differently.
• Madder root: 50–100g of chopped or powdered root for a medium red. Powdered madder releases colour faster but is gritty, so strain it through a fine cloth.

Soak madder root overnight in cold water before use. This draws out the red and leaves some of the browner pigments behind, giving a cleaner, brighter result.

Mordanting: The Step That Decides Everything

Scour the wool first — a warm soak with a pH-neutral wool wash, no detergent and no sudden temperature changes, or you will felt it. Then mordant.

For 100g of dry wool, dissolve 10–12g of alum (potassium aluminium sulphate) and 5g of cream of tartar in hot water. Top up the pot so the wool can move freely, add the damp wool and hold at 80–85°C for an hour. Do not boil it. Let the pot cool overnight, then squeeze out the excess — do not rinse.

Keep pans, spoons and a thermometer for dyeing only.

Dyeing with Onion Skins

Simmer the skins in water for 30–45 minutes, then strain them out. Add the mordanted, still-damp wool and hold at 80°C for an hour. Brown onion skins with alum give that familiar warm apricot, deepening to amber if you leave the wool in the pot overnight as it cools. A little extra cream of tartar pushes it toward gold.

Red onion skins are the surprise. With alum they usually land somewhere between khaki and soft olive, sometimes with a pink cast in the highlights. An acid rinse — a splash of vinegar in the final cooling water — warms them up considerably.

Dyeing with Madder: Keep It Below a Simmer

Madder is fussier about heat than onion skins, and the difference is dramatic. Above roughly 60°C the red begins to turn brown and muddy, so keep the pot well below a simmer. A thermometer is worth the small outlay.

Add the soaked madder to the bath, warm gently to 50–60°C and hold for an hour, stirring only occasionally and gently. Madder likes calcium and slightly alkaline water — a teaspoon of chalk or a pinch of washing soda helps the red develop in soft-water areas. Lift the wool out while the bath is still warm rather than letting it cool overnight in the dye, which can dull the colour.

Shifting the Colour and Making It Last

Once the wool is out, a small amount of modifier can transform what you have.

• Iron: 1–2g of ferrous sulphate per 100g of wool saddens onion orange to deep rust and turns madder red to aubergine-brown. Add it gradually; too much makes wool brittle.
• Acid: a splash of vinegar brightens and warms both dyes, and helps the last of the colour exhaust onto the fibre.
• Alkaline: washing soda shifts madder toward rose and onion skins toward gold.

Rinse in water of the same temperature as the bath, wash cool with a pH-neutral soap, and dry in the shade. Madder is famously lightfast; onion skins fade more in strong sun, so store finished work away from a bright window. Keep notes — weight of fibre, mordant, temperature, timings — and you can repeat any result exactly. That notebook, more than any recipe, is what turns a lucky dip into a craft.