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Alum Rock Crystal | Lesley Darling Fiber
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Alum Rock Crystal

Alum Rock Crystal

Alum is a mineral mordant used to help dyes bind to fiber. It's also used in pickles! And papermaking! In use since Ancient Egyptian times and beyond.

This rock form of alum avoids any dusts. Also just looks cool on the shelf! You can dissolve the whole crystal in a liter of water to make a concentrated stock solution for mordant baths. Email me with any questions! Each rock is uniquely shaped, and each "order" includes ~100 g of alum, which may be more than one rock.

I typically use 10% alum for the weight of fibers to be mordanted. When dyeing cellulose, I give the fibers a tannin bath beforehand (see our wildforaged sumac). You may see a flocculate or cloudy appearance in the water: this is just the alum causing the minerals in your water to condense. Cool huh?

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