Alum Mordant

Potassium Aluminium Sulphate Dodecahydrate

Potassium Alum is the most commonly used mordant for wool, silk and many natural dyes. It helps suitable plant dyes bond with the fibre and generally produces clear, bright colours without darkening them.

For protein fibres, use 7.5–15% WOF - weight of dry fibre.

Cotton, linen and other cellulose fibres require a different mordanting method. Alum should not be used alone on cellulose.

At a glance

How much to use

For wool and other protein fibres, begin with:

• 7.5% WOF for paler shades or minimum mordant residue
• 10% WOF as a general starting point
• 12–15% WOF for deeper shades

WOF means weight of dry fibre. For example, 10% WOF is 10g Alum for 100g dry fibre.

More Alum does not automatically produce stronger or more colourfast results. Use the lowest amount that works well for your fibre and dye.

Cold mordanting wool

Cold mordanting is our preferred method for wool.

1. Weigh the dry fibre and calculate 7.5–15% WOF Alum.
2. Soak the fibre thoroughly in water.
3. Dissolve Alum in a small amount of hot water.
4. Add it to a container of cool water and stir.
5. Add the wetted fibre and ensure it is fully immersed.
6. Leave for 24–72+ hours, moving the fibre occasionally.
7. Remove, rinse and dye immediately, or dry for future use.

Cream of tartar is not required for cold mordanting.

Hot mordanting wool

1. Weigh the dry fibre and calculate 7.5–15% WOF Alum.
2. Soak the fibre thoroughly.
3. Dissolve the Alum in hot water and add it to the mordanting pot.
4. Optional: add up to 5% WOF cream of tartar.
5. Add the wetted fibre.
6. Slowly raise the bath to approximately 80°C.
7. Hold for one hour, moving the fibre gently.
8. Allow it to cool before rinsing.

Avoid boiling or excessive movement, as this may felt wool.

Silk

For silk, begin with 7.5–10% WOF Alum.

Cold mordanting is particularly suitable. Handle delicate silk gently and sample first.

Cotton, linen and other cellulose fibres

Alum alone is not a complete mordant for cellulose fibres.

For cotton, linen and hemp, use one of our complete cellulose methods:

• Tannin followed by Alum and soda ash
• Aluminium acetate followed by chalk

Do not use the wool recipe directly on cotton or linen.

Good to know

• Dissolve Alum completely before adding the fibre.
• Wet the fibre thoroughly for even uptake.
• Alum is not required for indigo or woad vats.
• When layering indigo with mordanted colours, apply indigo first.
• Alum supports many natural dyes but cannot make a naturally fugitive colour permanent.
• Used mordant baths may retain Alum and can often be saved for reuse.

Storage and safe handling

• Store sealed in a cool, dry place.
• Avoid creating or breathing dust.
• Wear eye protection when handling powder or concentrated solutions.
• Wear gloves where appropriate.
• For textile dyeing and craft use only.
• Not for consumption or cosmetic use.
• Use dedicated dyeing equipment.
• Keep away from food, children and pets.
• Do not release concentrated solutions into drains or natural waterways.

What you receive

Your chosen net weight of potassium aluminium sulphate dodecahydrate, supplied in a sealed pouch.

Cream of tartar, soda ash, tannins and other dyeing materials are sold separately.

Display jars, dyed fibres and photographic props are not included.

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IRON MORDANT ~ Mordant, Colour Changer, increased light fastness

Iron (Ferrous Sulfate) is used alone as a mordant, influencing Colours and to increase light fastness when used in combination with other natural dyes.

Iron is best known for shifting yellows into greens, keep in mind that this is not given and doesn't work with every yellow plant dye, in which case it will be more of a brown. it is used to increase light fastness for weaker plant dyes, bu it will always sadden and/or darken the colours. 

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Basic recipe:

When adding Iron to your dye bath start of with 3% and use it at the end of your dye bath or as an after bath. Allow to oxidize for 10 min for full colour development.

*If you like your colours darker, increase the Iron amount by 1-2% at a time. 

**Leave for 10min than remove from dye bath - Iron will make wool brittle.

Sodium Acetate ~ Used to turn Ferrous Sulfate into Ferrous Acetate; used in the Mordanting Recipe for Cotton and Linen without Tannin (see below)

Sodium acetate, NaCH₃COO, also abbreviated NaOAc, is the sodium salt of acetic acid. We use Sodium Acetate to turn Iron into an easier digestible version of itself, Iron acetate. Similar to 'Iron Water' but you can control the amounts. Iron acetate is not as harsh on the fibres and can be easier digested by nature or your septic tank when turned into rust. Once made, it has no shelf life and needs to be used immediately. 

For mordanting Cellulose fibres, please choose one of the following recipes on our blog:

How to mordant linen and cotton fabrics successfully – AppleOak FibreWorks

How to mordant Linen and Cotton successfully without Tannins – AppleOak FibreWorks

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Basic recipe: 

1part Ferrous Sulfate

1part Sodium Acetate

Mix and dissolve in Water. I find that it makes the iron stronger and we only use 1% of Iron acetate on most recipes. Warm water will also intensify the reaction.

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Aluminium Lactate Mordant

For Linen, Cotton, Hemp & Other Cellulose Fibres

Aluminium lactate is a modern mordant for cotton, linen, hemp, ramie, nettle and other cellulose fibres.

It dissolves in water at room temperature and can produce bright, clear colours without requiring a heated mordant bath.

For the most reliable colour uptake and durability, we recommend applying a tannin treatment first, followed by 5–8% WOF aluminium lactate.

At a glance

How much to use

Use:

5–8g aluminium lactate per 100g dry fibre

Equivalent to 5–8% WOF - weight of dry fibre.

Suggested method

Stage one: Tannin

1. Scour the cotton, linen or other cellulose fibre thoroughly.
2. Apply a suitable tannin treatment.
3. Remove the fibre and gently squeeze or spin out the excess liquid.
4. Do not rinse aggressively or allow the fibre to dry.

Low-colour tannins include:

• Tara
• Oak gall
• Sumac gallnut

For a warmer background colour, use Myrobalan, acacia or chestnut.

Stage two: Aluminium lactate

1. Calculate 5–8% WOF aluminium lactate.
2. Dissolve the powder completely in room-temperature water.
3. Add enough water for the fibre to move freely.
4. Add the damp, tannin-treated fibre.
5. Leave for 1–2 hours, moving the fibre occasionally. It may also be left longer or overnight.
6. Remove and rinse thoroughly.
7. Dye immediately or dry the prepared fibre for later use.

A chalk bath is not part of our tannin and aluminium lactate method.

Why we recommend tannin first

Cellulose fibres have relatively few natural binding sites for aluminium mordants.

The tannin and aluminium stages work together. During the aluminium lactate stage, the tannins are converted into insoluble tannates within the fibre.

Aluminium lactate can be used without tannin, but we recommend the complete tannin-first process where wash fastness and long-term durability are priorities.

Find our cellulose mordanting information here.

About this mordant

The lactic acid used to produce this aluminium lactate is obtained through fermentation of renewable sugar- or starch-industry materials.

The supplier’s Aluminium Lactate received approval as a textile mordant input under GOTS 6.0. This does not automatically make the finished textile GOTS-certified.

Good to know

• Aluminium lactate dissolves at room temperature.
• A heated mordant bath is not required.
• Use it primarily on cellulose fibres.
• Use Alum for most wool and silk mordanting.
• Indigo and woad do not require mordanting.
• When combining indigo with mordanted colours, apply indigo first to protect the vat from contamination.
• Always sample before beginning an important project.

Storage and safe handling

• Store sealed in a cool, dry place.
• Protect from humidity.
• Avoid creating or breathing dust.
• Work in a well-ventilated area.
• Wear gloves, eye protection and suitable respiratory protection when handling the powder.
• Avoid contact with the skin and eyes.
• For textile dyeing and craft use only.
• Not for consumption or cosmetic use.
• Use dedicated dyeing equipment.
• Keep away from food, children and pets.
• Do not release concentrated solutions into drains or natural waterways.

What you receive

Your chosen net weight of aluminium lactate powder, supplied in a sealed pouch.

Tannins, dyes and other mordanting materials are sold separately.

Display jars, dyed textiles and photographic props are not included.

Learn with us

Join The Natural Dyers & Growers Academy to share your results and explore natural colour alongside fellow dyers and growers.