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Alum (Potassium Aluminum Sulfate)

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Alum (Potassium Aluminum Sulfate, KAl(SO₄)₂·12H₂O)

Also known as alum, potassium alum, potash alum.

Alum is the most widely used mordant in natural dyeing. Gentle yet highly effective, it allows natural dyes to bond securely to fibres, producing brighter shades with improved wash- and lightfastness. Alum is widely used and comparatively gentle on fibres, but the dry powder and mordant solution still require careful handling.

Historical Note
Alum has been prized since antiquity. The earliest recorded sources were natural mineral deposits in Asia Minor, especially around the island of Melos in Greece and in regions of present-day Turkey. By the Middle Ages, the alum trade became a central part of the dye industry, with major production sites in the Middle East and later in Italy. The Tolfa mines near Rome supplied alum to Europe for centuries, and alum was often controlled as a strategic commodity by states and guilds.

Traditionally, alum was obtained by mining alum-rich shale, leaching with water, and purifying by crystallization. Modern alum is produced by processing bauxite with sulfuric acid, yielding the crystalline hydrate that continues to serve as the cornerstone mordant for natural dyeing.

Active Compound
Potassium aluminum sulfate dodecahydrate.

CI Reference
Used as a mordant; not classified as a dye.

Advantages

Produces bright, clear shades
Improves both wash fastness and light fastness
Gentle on fibres compared to other metallic mordants
Works on both protein and cellulose fibres (the latter usually with a tannin base first)

Safety & handling

For textile dyeing and craft use only. Not for food, cosmetic, medical or household-cleaning use.

Avoid contact with skin and eyes. Powder and solutions may cause irritation.
Do not release concentrated product or spent mordant baths into drains, soil or waterways.
Keep out of reach of children and pets.
Avoid creating or breathing dust. Measure carefully in a well-ventilated work area and use suitable respiratory protection for fine particulates when dust cannot be avoided.
Wear suitable protective gloves, protective clothing and eye protection. Wash hands thoroughly after handling.
Do not eat, drink or smoke while using this product. Use dedicated tools and containers that will never be used for food.
Store tightly closed, dry, clearly labelled and away from food, drink and incompatible materials.
Eyes: Rinse cautiously with clean water for several minutes. Remove contact lenses if easy to do and continue rinsing. Seek urgent medical advice for persistent irritation, pain or impaired vision.
Swallowed or inhaled: Move to fresh air after inhalation. If swallowed, rinse the mouth and contact a poison centre or medical professional; do not induce vomiting unless instructed.

Important: Follow the package label and the current Safety Data Sheet for the exact product. Formal hazard classification can depend on chemical form, hydration, purity and composition. For the latest safety documentation, contact info@naturaldyestore.com.

Seller and safety contact: Natural Dye Store, Derech HaMaccabim 58, Rishon LeZion, Israel · info@naturaldyestore.com

Dosage:

Protein fibres → 15–20% WOF

Cellulose fibres → tannin 10% WOF followed by alum 10%

Dissolve: always dissolve completely in hot water before adding to mordant bath

Mordanting:

Pre-wet fibres.

Add to alum solution and heat gently (60–70 °C).

Hold for 45–60 minutes with occasional stirring.

Cool in the bath for best uptake.

Rinse

Fibres are now ready for dyeing.

For external use only. Not edible.
Keep away from children and pets.
Wear gloves and mask when handling powders.
Avoid inhalation of dust and contact with eyes.

Store in a cool, dry place away from direct sunlight. Reseal tightly after use.

Naturally derived and carefully processed from trusted sources to ensure safe use in dyeing and textile applications.

This product complies with the General Product Safety Regulation (EU) 2023/988 (GPSR).

Packed and distributed by The Natural Dye Store, eHouse Rishon, Derech HaMaccabim 58, 7535998 Rishon LeZion, Israel. Contact: Suzanne Tamar Dekel, info@naturaldyestore.com, +972 52-541-0033.