Mordant calculator, percent of fiber weight.
Weigh the dry fiber, choose wool, silk or cotton, and get the grams of alum, cream of tartar, tannin and iron, plus how much dye material to gather.
The fiber
Percentages of fiber weight
Common starting points; recipes differ by book and by dyer. Edit them to match the one you follow.
Weight of fiber
Every natural dye recipe is written as a percentage of the dry fiber weight, written WOF: 12 percent alum means 12 grams of alum for every 100 grams of dry wool. Weigh the fiber dry before you scour it, write the number on a tag, and every bath that follows is a multiplication. The amount of water does not matter beyond covering the fiber freely.
Protein and cellulose
Wool and silk take alum directly: one bath of alum, with cream of tartar for wool, and they are ready for the dye pot. Cotton, linen and hemp hold alum poorly on their own, so they are tannined first, then alumed, often with a little soda ash, and sometimes the pair is repeated. The result is a cellulose fiber that takes most plant dyes nearly as well as wool.
How much plant material
- Strong dyes (madder root, weld, cutch, dried marigold): 50 to 100 percent WOF.
- Middling dyes (onion skins, dried coreopsis, black walnut hulls): about 50 percent, though onion skins give a strong color at less.
- Weak or fresh material (leaves, fresh flowers, avocado stones): 100 to 200 percent WOF, or more.
- Iron at 1 to 2 percent shifts yellows to olive and pinks to gray; more than 4 percent weakens wool over time.
Alum and cream of tartar are low-hazard but not food; iron sulfate stains and irritates; keep every dye chemical labeled, out of reach of children, and used in dedicated pots. The natural dyeing page has the starter kit and the first project.