Hemp takes colour beautifully and almost every failure happens before the dye pot. It is a cellulose fibre with a lot of natural residue on it, so scouring and mordanting are not optional steps — they are the job.
Five steps and only one of them is dyeing. Skipping steps two or three is why colour comes out patchy or washes straight back out.
Simmer the fabric an hour with soda ash and a little detergent, then rinse until the water runs clear. Hemp carries pectins, waxes and mill finishes that repel dye. This is the step people skip and the reason for most blotchy results.
Cellulose does not bind metal mordants the way wool does, so it needs a bridge. Soak in a tannin bath — oak gall, myrobalan, or strong tea — overnight. Myrobalan gives a pale buff; oak gall is nearly clear.
Aluminium acetate for cellulose, warm, an hour, then rinse. Alum sulphate works less well on plant fibre — this is the one place where using the wool chemistry gives a visibly worse result.
Bring to a simmer with the dyestuff and hold it, moving the cloth. Longer and cooler beats hotter and faster for evenness. Let it cool in the pot overnight for the deepest shade.
Rinse cool until clear, wash with a pH-neutral soap, dry in shade. Leave it a week before washing it properly — the bond keeps developing after the pot.
| Dyestuff | Colour on hemp | Lightfastness | Notes |
|---|---|---|---|
| Madder root | Warm red to terracotta | Excellent | Keep below 70 °C or it browns |
| Weld | Clear bright yellow | Very good | The best yellow for cellulose |
| Indigo | Blue, any depth | Excellent | A vat, not a dye bath — no mordant needed |
| Walnut hull | Warm brown | Good | Substantive; works with no mordant |
| Logwood | Purple to grey-black | Moderate | Shifts with pH; fades in strong sun |
| Onion skin | Gold to bronze | Moderate | Free, and the easiest first dye |
| Avocado stone | Dusty pink | Moderate | Also free; results vary widely |
Fabric softener coats the fibre and blocks dye entirely. Cloth that has been washed with it cannot be reliably dyed afterwards, and no amount of scouring fully removes it.
Check before you buy second-handNatural dyeing is measured as a percentage of the dry weight of fibre — 20% madder means 20 g of madder per 100 g of cloth. Guessing is why a batch cannot be repeated.
Write it down every timeIt is not dissolved and it is not mordanted — it is reduced in a vat and oxidises on the air, turning from yellow-green to blue in front of you. Worth learning separately.
No mordant, no simmerUnder-scoured, nearly always. Second most likely is too little water in the pot, so the cloth could not move freely. Both are fixable on the next attempt and neither is the dye's fault.
On walnut and other substantive dyes, yes. On madder, weld and most others you will get a paler, less washfast result. Tannin is what gives cellulose something for the mordant to hold.
Properly mordanted madder, weld and indigo on hemp are genuinely durable — historic textiles prove it. Wash cool, dry in shade, and expect gentle shifting over years, which is most of the appeal.
Use a dedicated stainless or enamel pot. Iron and copper shift colours markedly — sometimes usefully — and mordant chemicals should not share pans with food.