Collect a quantity of skins from brown and red (Spanish) onions. Have ready a piece of silk — habutai or crêpe de chine works well.
Lay the silk flat on the work surface and spread the onion skins over the silk.
Moisten using a hand-mister filled with vinegar (or any of the non-toxic home- made mordants). Starting at one edge, roll the silk with the onion skins inside.
When you have a sausage shape, roll that up as well. Tie tightly with string or fasten with rubber bands. Moisten the outside with a little more liquid, bundle in a plastic bag (or place in a jar with lid), and set aside for at least a week, preferably one month.
If mould appears, place the object in a snap-lock bag and freeze for a few days. Alternatively, steam it over boiling water for 30 minutes.
Unwrap, shaking off the plant material (this is best done outside in the garden if you have one).
Allow to dry, then press with a steam iron (use a pressing cloth). Allow to rest at least a few days before first rinsing.
The most difficult thing about this method is resisting opening the bundle to check on the colour!
Post-mordant in an iron-rich solution (or spray on using the hand-mister) and observe the colours change to olive greens and browns.