Mordant Reference Chart
These are craft-practice conventions gathered from fiber-arts educators, not a regulated standard — treat every figure below as a well-sourced starting point, not a guaranteed-safe universal number. This chart covers dose only: temperature and timing (how hot, how long, how the fiber is cured afterward) also materially affect the result and aren’t covered by the calculators on this site.
Alum mordant
“Alum” covers two different aluminum salts used in craft practice at overlapping but not identical doses — aluminum potassium sulfate (potash alum) and aluminum sulfate. They aren’t 1:1 substitutes by weight (aluminum sulfate delivers more aluminum per gram), but published craft ranges for both overlap enough that one default below is a reasonable starting point for either.
| Fiber category | Alum (% WOF) | Water bath |
|---|---|---|
| Protein (wool, silk, alpaca, mohair) | 10–20% (12% typical) | 3–6 L per 100 g fiber |
| Cellulose (cotton, linen, hemp, ramie) | 15–20%, plus 2% soda ash (required) | 5–7 L per 100 g fiber |
Protein fiber process is temperature-critical (ramp to roughly 90°C for wool, 85°C for silk, hold about an hour, then cure damp 24–48h) — not just the dose above.
Soda ash (cellulose alum step — required, not optional)
Added alongside alum in the same bath for cellulose fibers. It’s what allows aluminum to deposit onto tannin-treated cellulose — an alum bath without it fixes poorly. Mildly alkaline; dissolve fully in hot water before adding to the mordant bath.
Dose: 2% WOF.
Tannin pre-mordant (cellulose fibers only)
Applied before the alum + soda-ash step. Cellulose fibers lack the binding sites protein fibers have, so skipping this step is possible but the resulting color typically fades faster. Different tannins need materially different doses — they are not interchangeable at one percentage.
| Tannin | Dose (% WOF) |
|---|---|
| Myrobalan | 15–20% |
| Gallnut extract | 6–8% |
Water bath: ~3 L per 100 g fiber (≈30:1). Tannin type also affects color cast — gallic tannins (gallnut) read close to colorless, ellagic tannins (myrobalan) read yellow.
Cream of tartar (optional, protein fibers)
Added alongside alum for wool or silk. Assists the alum in binding to the fiber and can keep it softer. Any color effect is dye-specific, not a universal brightening — for example it shifts madder toward orange and cochineal toward a brighter red. No equivalent step exists for cellulose fibers.
Typical dose: 5–6% WOF (6% is the most commonly cited figure).
Iron modifier (ferrous sulfate, post-dye)
Used after dyeing to “sadden” (darken/mute) a color, not as a primary mordant. The cited source uses iron at 2% WOF in its own color samples and states it should never be used above 4% WOF — excess iron makes fiber brittle, especially wool and silk.
| Dose | Guidance |
|---|---|
| 2% WOF | The cited source’s own sample dose. |
| Above 4% WOF | Explicitly not recommended by the cited source — real fiber-damage risk. |
Iron powder is harmful if swallowed — wear a dust mask when weighing it, keep it away from children and pets, and dispose of the used bath down a municipal or septic drain, never into a stream, lake, or other waterway.
Sources
- naturaldyes.ca (Maiwa) — “How to Mordant: Protein Fibres,” “How to Mordant: Cellulose Fibres,” “Iron,” “Myrobalan,” “Gallnut,” and “Mordants” — alum/soda-ash/tannin/iron dosing, water ratios, and the case against chrome/tin/copper mordants.
- Botanical Colors — “How to Mordant with Aluminum Sulfate,” “How to Mordant with Aluminum Potassium Sulfate,” and “How To Use Iron Powder” — alum dose ranges, cream of tartar dose, iron safety/disposal guidance (reproduced by Dharma Trading Co.’s iron mordant instructions).
Retrieved 2026-09-14, cross-checked via an independent domain-expert review the same day.