Natural Dye Mordant Ratio Calculator
Get the right mordant-to-fiber ratio using the Weight of Fiber (WOF) system dyers have relied on for generations.
How this calculator works
The Weight of Fiber (WOF) system expresses mordant quantity as a percentage of your fiber's dry weight — scale-independent, so the same percentage works whether you're dyeing 50 grams of thread or 5 kilograms of cloth. This tool applies the standard percentage for your chosen mordant, then recommends a water bath volume: 30:1 water-to-fiber by weight for most mordants, 40:1 for iron, since even distribution matters more there to avoid blotchy, over-dark spots.
Where these numbers come from
- Alum at 10–20% WOF (15% typical): Botanical Colors and AppleOak FibreWorks mordanting guides, consistent with each other
- Copper at 2–4% WOF, iron used sparingly to avoid dulling/embrittling fiber: Kraft Kolour natural dye reference
- 30:1 (40:1 for iron) water-to-fiber bath ratio: standard natural-dyeing practice
Iron and copper mordants are more aggressive than alum — overuse can weaken protein fibers over time. Alum is the standard safe default for most projects.
Frequently asked questions
What does "Weight of Fiber" (WOF) actually mean?
It's a dyeing convention where the mordant amount is calculated as a percentage of your dry fiber's weight, not the water volume — so a 10% WOF mordant on a pound of fiber means the same amount of mordant regardless of how much water it's dissolved in.
Why does mordant ratio matter for natural dyeing?
Mordant helps the dye actually bind to the fiber instead of washing out — too little and color fades quickly, too much can damage certain fibers or waste mordant, so hitting the right WOF percentage matters for both color fastness and fiber safety.
Does the right ratio change by fiber type?
Yes — protein fibers like wool and plant fibers like cotton often call for different mordant types and percentages in traditional natural dyeing practice, so match your mordant choice and ratio to the specific fiber you're working with.
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