Aluminum Potassium Sulfate




Highly prized worldwide since antiquity, Aluminum Potassium Sulfate is the premier mordanting material for protein fibers such as silk and wool. What does this humble mineral have in common with the most powerful family in Italy during the Renaissance? During the 12th century, ambitious nobles and merchants became rich on alum exports from the Aegean islands.  In the mid-15th century, the expanding Turkish empire gained control of the Aegean areas and imposed heavy tariffs on the mineral, causing a shortage and a sharp spike in prices in Italy.

Around the same time, rich alum veins were discovered near Tolfa outside of Rome and within the Papal States of Italy. Pope Pius II seized the opportunity to export alum and build the Vatican fortune throughout Christendom. The Medici bankers, financiers and cultural influencers, also grew their fortune on wool textile manufacturing in Florence, requiring Tolfa alum. Italy exported alum throughout Europe for nearly 300 years until competition from other sources arose in the 18th century.  So what does this wondrous substance look like? Aluminum potassium sulfate is refined from bauxite and is a transparent, free flowing crystal, resembling salt. We supply a food grade aluminum potassium sulfate that is free of iron and other impurities.

You can use between 10-20% alum on the weight of fiber.  250 grams will mordant about 2500 grams (5.5 lbs) at 10%  Aluminum potassium sulfate dye baths may be used either hot or cold, and may also be re-used with the addition of more alum.  Check out our How To Mordant section for further information.

Check out our How To Mordant instructions for detailed information on preparing your fibers for natural dyeing.

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Weight N/A
Dimensions N/A

250 gm, 500 gm, 1000 gm