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 | 100% | Warm golden yellow |
| Weld (reseda) | 75% | Clear, bright yellow |
| Madder root | 75% | Warm reds and oranges |
| Black walnut hulls | 150% | Rich warm browns |
| Chamomile | 100% | Soft yellow |
| Hibiscus | 100% | Pink to burgundy |
| Woad | 50% | Pale to medium blue |
Indigo is not on that list on purpose. It does not dissolve in water and cannot be simmered like the others. It needs a reduction vat, where the dye is chemically converted to a soluble form, the fibre is dipped, and the colour develops in the air as it oxidises. The quantities and the whole method are different enough that a percentage on this page would be misleading. Woad is included because although it contains the same pigment, small-scale woad dyeing is usually done as a simple steep.
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)
How much water
Fibre needs room to move, or it dyes in patches wherever it presses against itself. Use 25 to 30 times the fibre weight in water, so 100 g of wool wants around 2.75 litres. This is one of the few numbers where more is genuinely safer: a crowded pot is the most common cause of blotchy results.
Safety, specifically for iron and copper
Alum and tannin are benign. Iron (ferrous sulfate) and especially copper sulfate are not. Copper sulfate is toxic to people and severely toxic to fish and aquatic life; iron is an irritant and stains permanently.
Keep a pot, spoons and jars used only for dyeing and never returned to the kitchen. Wear gloves, open a window, and do not tip an exhausted metallic bath down a drain that reaches a watercourse. Check what your local authority requires for disposal, because it varies and the answer is rarely “the sink”. None of this makes these mordants unusable, it just means treating them as the chemicals they are rather than as craft supplies.
How we build and check this calculator
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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