Scientific WOF ratios for fixing natural dyes to vegan fibers — sourced from 1882 textile standards
Quick Presets
Weigh fiber while completely dry — this is your Weight of Fiber (WOF) baseline.
Fiber Material (Vegan)
Mordant Agent
Alum brightens · Iron saddens/darkens · Tannin pre-treats cellulose
Mordant Required:
20 grams
Water Bath Volume:
3 liters
% WOF Applied:
20 %
Data Source: The Dyer's Companion (1882) • Public domain • Solo-developed with AI
🌿 Dye Plant Quick Reference
| Plant / Source | Color Result | Best Mordant | Notes |
|---|---|---|---|
| Onion Skins (yellow) | Rich gold / amber | Alum | Most beginner-friendly; very high dye yield |
| Marigold (Calendula) | Warm yellow / gold | Alum | Fresh or dried; use 100–200% WOF flowers |
| Weld (Reseda luteola) | Bright chartreuse | Alum | Best lightfast yellow available to natural dyers |
| Black Walnut Hulls | Warm dark brown | None / Iron | Self-mordanting tannins; iron deepens to near-black |
| Madder (Rubia) | Coral to brick red | Alum | Simmer at ≤80°C to preserve reds; boiling yields brown |
| Chamomile (dried) | Pale gold | Alum | Light, delicate shade; good for overdyeing pastels |
| St John's Wort | Golden yellow-green | Alum | Harvest in bloom; use 150% WOF; iron shifts to olive |
| Woad (Isatis) | Pale to medium blue | None | Vat dye — no mordant needed; very different process |
| Sumac Leaves | Tan to warm beige | Tannin / Alum | Rich in tannins; excellent pre-mordant source itself |
| Nettle (Urtica) | Pale greenish-yellow | Alum | Use 150% WOF; also a fiber plant — versatile |
🎯 A Simple Example: Botanical Mordant Calculator — Step by Step
You've foraged a bag of onion skins and have a plain 150g cotton tote bag you want to dye gold. You need to mordant the fiber first so the color bonds permanently.
Just do this:
1️⃣ Click the Onion Skin Gold preset — or enter "150" in the Weight field and select Cotton + Alum
2️⃣ The tool shows you need 30.0 g Alum in 4.5 L water (20% WOF)
3️⃣ Dissolve alum fully in hot water in a stainless pot, then submerge the wet tote bag
4️⃣ Simmer gently for 45–60 minutes, then let cool in the bath and rinse
5️⃣ Move directly to your onion skin dye bath — the mordanted fiber is now ready to grab color!
Pro tip: Always weigh fiber dry. Wet fiber weighs more and will throw off your WOF calculation, leaving you with too little mordant and fugitive colors.
Why Mordanting Exists. Natural plant dyes rarely bond directly to cellulose fibers like cotton, linen, or hemp — they lack the protein "hooks" that wool and silk possess. A mordant (from Latin mordere, "to bite") solves this by bridging the gap: metallic ions from alum or iron form a coordination complex with both the fiber and the dye molecule, locking color in place permanently. Without a mordant, even the richest marigold bath will wash pale after a single rinse.
Alum vs. Iron vs. Tannin — When to Use Which. Potassium alum (20–25% WOF) is the workhorse: it brightens and clarifies colors, is safe to handle, and is the default choice for all vegan fibers. Ferrous sulfate / iron (2–3% WOF) is powerful but must be used sparingly — it "saddens" hues (shifts yellows to olive, reds to brown-grey) and can degrade fibers if overdosed. Tannin pre-mordant (6–10% WOF, from oak galls, sumac, or black tea) is not a mordant itself but opens cellulose for deeper alum uptake — essential for achieving rich, dark shades on cotton or bamboo that otherwise resist color.
The WOF System — 1882 to Now. The Dyer's Companion (1882) established the "Weight of Goods" percentage system still in universal use today. All ratios are expressed as a fraction of dry fiber weight, making them scale-independent: 20% WOF works equally whether you're dyeing 50 g or 5 kg. This calculator converts those Victorian proportions directly — multiply your dry fiber weight by the mordant percentage and you have grams of mordant to dissolve, no further maths needed.
Water Volume Matters. The 30:1 water-to-fiber ratio (30 mL per gram of fiber) is the minimum recommended for free movement in the bath. Too little water causes uneven mordanting and streaking; the fiber must be able to circulate and remain fully submerged throughout the simmer. For dark or iron mordanting where even distribution is critical, consider 40:1 to give yourself extra margin.
🐾 From the Lab Cat's Department of Suspicious Liquids: The humans boiled something that smelled of onion skins and then dunked a perfectly innocent cotton bag into brown tea water they called "tannin pre-mordant." I sat on the bag to test color fastness. Result: excellent. The gold stain transferred to my white belly fur with outstanding permanence. I give this process five stars and zero regrets. Next experiment: the iron pot. I am told it will make things darker. I support this. 🌿