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)
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This calculator runs entirely in your browser, so the numbers you enter stay on your device. The math behind it is written by hand and tested against worked examples and standard references before the page goes live.
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