Natural Dye Calculator (Weight of Fibre, Mordant %, Dyestuff by Shade Depth, Bath Volume)
Scale a natural dye recipe to your fibre: alum, cream of tartar or tannin mordant amounts from the weight of fibre for wool, silk or cotton, the dyestuff needed for a light, medium or deep shade, bath volume at the right liquor ratio, and iron or copper modifier amounts.
How it works
everything is a percentage of the dry weight of fibre (WOF) · wool: alum 12% + cream of tartar 6%; silk: alum 8%; cellulose: tannin 8% then aluminium acetate 8% (or alum 15% + soda ash 2%) · dyestuff % WOF by depth (madder 25/50/100, weld 25/50/100, cochineal 3/6/12, logwood 10/25/50, onion 50/100/200, extracts 2/5/10…) · bath = WOF × liquor ratio (30:1) in litres
Natural dyeing is written in percentages of the dry weight of fibre, which is what makes recipes scale: the mordant that lets the dye bond, the dyestuff that sets the depth of colour, and any modifier that shifts the hue are all a fraction of the grams of yarn or cloth going into the pot. Protein fibres (wool, silk) take alum directly; cellulose (cotton, linen) needs a tannin step first or the colour rinses away. The water is sized to let the fibre move — too crowded a pot dyes unevenly. This calculator turns your fibre weight and chosen dye into gram amounts for each bath.
Worked example
For 200 g of wool in madder at a medium shade: mordant with 24 g of alum and 12 g of cream of tartar in a 6 L bath, then dye with 100 g of madder root (50% WOF) in 6 L kept under 70 °C, and cool overnight. An iron after-bath of 4 g would sadden the red to brick; the exhaust bath will still dye another 200 g to a soft coral.
Frequently asked questions
Do I really need a mordant?
For most plant dyes on wool and cotton, yes — without it colour is weak and washes out. Exceptions are substantive dyes with their own tannins (walnut, some barks, tea, cutch) and vat dyes (indigo, woad). Alum is the safe general mordant; avoid chrome and tin.
Why is my cotton so much paler than my wool from the same pot?
Cellulose fibres bond poorly with alum alone. Scour thoroughly (cotton carries waxes), tannin-mordant first, then aluminium acetate, and use more dyestuff or a longer, warmer bath. Even so, cotton typically takes 30–50% less colour than wool.
How do I get consistent, repeatable colour?
Weigh everything (fibre dry, mordant, dye), use the same water source and liquor ratio, control temperature and time, and keep a dye journal with a sample. Natural dyestuffs vary by harvest, so test a small skein from each new batch of dye material.
Related calculators
Fibre-craft estimates depend on your tension, yarn, stitch pattern and blocking. Always knit or crochet a gauge swatch, wash and block it as you will the finished piece, and measure from that. Mordants and modifiers are chemicals: wear gloves and a mask for powders, use dedicated pots and utensils never used for food, keep them from children and pets, and dispose of baths responsibly.