Before you start

• Always scour and fully wet out your yarn or fabric first so the mordant can penetrate evenly.​

• Use non‑reactive pots (stainless steel or enamel), measure mordant by weight of fiber (WOF), and keep good notes so you can repeat results.​

Wool and other protein fibers

1. Weigh your dry fiber, calculate alum (often around 10–15% of WOF) and, if desired, a little cream of tartar (about 5–6% WOF).​

2. Dissolve the alum (and cream of tartar) in a small amount of boiling water, then add this solution to a larger pot of warm water, stirring well.​

3. Add your pre‑soaked, wet wool to the warm mordant bath, making sure it can move freely and stay fully submerged.​​

4. Heat gently up to around hot‑but‑not‑boiling (often near 80–90 °C / 176–194 °F) and hold it there for about 45–60 minutes, stirring occasionally without rough agitation.​​

5. Turn off the heat and let the wool cool in the bath, then remove, squeeze out excess (you can save the bath to reuse), and rinse lightly or go straight to dyeing if your recipe calls for it.​

Silk (protein, but more delicate)

1. Weigh the dry silk and calculate alum (commonly around 10–15% WOF) as for wool.​

2. Dissolve the alum in hot water and add to warm (not boiling) water in your pot, mixing well.​

3. Add well‑wetted silk and keep it fully submerged, working it gently so the mordant reaches all areas.​

4. Keep the bath warm to gently warm/simmering, but below what you’d use for wool, and let the silk sit in the mordant for several hours or up to 24 hours without hard boiling.​

5. Remove the silk, squeeze out excess, then either rinse lightly and dye, or dry it to dye later (re‑wet thoroughly before dyeing).​

Cotton, linen, and other cellulose fibers (tannin + alum method)

1. Weigh the dry fiber, scour thoroughly, then fully wet it out; calculate tannin and alum amounts based on WOF following your chosen recipe.​

2. Make a tannin bath (for example with gallnut or other tannin) by dissolving tannin in hot water, adding enough warm water to cover the fibers, then immersing the wet cellulose and soaking 1–2 hours or longer, stirring occasionally.​​

3. Remove the fiber, gently squeeze and lightly rinse so it stays damp, then prepare the alum bath by dissolving alum (aluminum salt suitable for cellulose, like aluminum acetate or similar) in hot water and diluting with warm water in a clean pot.​

4. Add the tannin‑treated, wet fibers to the alum bath, making sure everything is submerged (weigh down if needed), and leave to soak several hours or up to 8–24 hours, stirring now and then.​

5. Take the fibers out, squeeze gently, rinse lightly, then dry or go directly to dyeing; some dyers repeat the alum step on cellulose for richer color.​

After mordanting

• Keep mordanted fibers labeled by fiber type, mordant, and date so you know what’s what later.​

• Mordanted yarn or fabric can often be stored dry; just wet it out well again before you put it into your dye bath so color penetrates evenly.​