Natural Fiber Dye Calculator
Calculate mordant and natural dye amounts for dyeing wool, silk, or cotton fabric.
Get the right ratios for a strong, lasting color.
Natural dyeing uses plant, animal, or mineral sources to color fiber. Unlike synthetic dyes, most natural dyes require a mordant — a mineral that bonds the dye to the fiber permanently.
What is a mordant?
A mordant (from Latin mordere, “to bite”) is a metallic salt that creates a chemical bridge between the dye molecule and the fiber. Without a mordant, most natural dyes wash out or fade quickly.
Common mordants:
| Mordant | Amount (% weight of fiber) | Effect on Color |
|---|---|---|
| Alum (potassium alum) | 10–20% | Brightest, truest colors, most common choice |
| Iron (ferrous sulfate) | 2–4% | Darkens and saddens colors, use sparingly |
| Copper (copper sulfate) | 2–3% | Greens and blue-greens, deepens color |
| Cream of tartar | 5–10% | Used with alum to brighten and soften fiber |
| Tannin (oak galls, tea) | 5–15% | Used to mordant cellulose fibers (cotton, linen) |
Natural dye amounts:
Most natural dyes use 50–200% weight of fiber (WOF) — meaning for every 100g of fiber, you use 50–200g of dye material.
| Dye Material | Amount (WOF) | Color |
|---|---|---|
| Onion skins (yellow) | 100% | Warm golden yellow |
| Weld (reseda) | 50–100% | Clear, bright yellow |
| Madder root | 50–100% | Warm reds and oranges |
| Indigo | 10–30% | Blues (special vat process) |
| Black walnut hulls | 100–200% | Rich warm browns |
| Chamomile | 100% | Soft yellow |
| Hibiscus | 100% | Pink to burgundy |
| Woad | 50% | Pale to medium blue |
The formula:
Mordant amount = Fiber weight (dry) × (mordant % ÷ 100)
Dye amount = Fiber weight (dry) × (WOF % ÷ 100)
Dyeing steps:
- Weigh dry fiber and calculate mordant amount
- Dissolve mordant in hot water, add fiber and simmer 45–60 minutes
- Cool, rinse fiber gently
- Prepare dye bath, simmer plant material 1 hour, strain out plant material
- Add mordanted fiber to dye bath, simmer 30–60 minutes
- Cool slowly in dye bath (don’t shock wool with cold water)
- Rinse in water of similar temperature, gently squeeze dry, don’t wring
Fiber type affects dye uptake:
- Protein fibers (wool, silk): Dye most easily, best color results
- Cellulose fibers (cotton, linen): Need a tannin pre-mordant before alum
- Synthetics: Do not take natural dyes (acrylics, nylon, polyester)