Alum (Aluminum sulphate)
$2.20 – $7.20
Used as a MORDANT in natural dyeing, which allows the plant pigments to bond with the fibres.
This is Potassium aluminum sulphate, the preferred form of alum for use as a mordant. This IS NOT pickling alum and should not be consumed.
Used mainly on protein fibres such as wool, alpaca, silk. Usually used in combination with cream of tartar. Many natural dyers do a premordanting of the fibre with alum, while others add it directly to the dyebath (particularly with loose fibre such as fleece). Also sometimes used in combination with tannic acid to premordant cellulose fibres such as cotton.
TO USE: calculate mordant required for 8 to 15% WOF (weight of fibre) and 4 to 6% WOF cream of tartar. Weigh and dissolve in hot water. Fill pot with sufficient water for the fibre to move, add alum and cream of tartar and stir. Enter fibre. Bring to 180-200°F and hold 1 hour. Stir yarns frequently but fleece only occasionally. Cool overnight, then wash in soapy water and rinse thoroughly. Dye immediately or dry the yarns to dye later.
Spent mordant solution may be safely disposed of down the drain (except for septic systems). It also may be poured around garden plants that prefer acidic soil conditions.
CAUTION: wear a mask when handling powders. Wear gloves when using alum, particularly when rinsing or handling wet yarns as it is very drying to the skin. Best done outdoors or with very good ventilation.