Quick answer: to dye fabric with Mimosa tenuiflora root bark, scour the fabric, simmer the bark in water for about an hour to make a dye bath, strain it, then keep the wet fabric in the warm bath for 45 to 60 minutes. Expect pinks, purples and reddish browns. The bark is rich in tannins, so it colours cotton and linen as well as wool and silk.
At a glance
| Bark needed | 25 to 100% of the dry fibre weight, depending on depth of shade |
|---|---|
| Water | About 30 parts water to 1 part fibre |
| Bath temperature | 80 to 90 °C (175 to 195 °F), never a hard boil |
| Time | About 1 hour to make the bath, then 45 to 60 minutes of dyeing |
| Fibres | Cotton, linen, wool and silk |
| Colours | Pinks, purples and reddish browns; grey-violet to charcoal with iron |
Why this bark works as a dye
Mimosa tenuiflora (also called Mimosa hostilis, tepezcohuite or jurema preta) has bark that is unusually high in condensed tannins. A 2022 study in the forestry journal Revista Árvore measured a condensed tannin content of 23.4% in the bark of the tree. Tannins bind readily to textile fibres, which is why tannin-rich barks have been used for dyeing and leather tanning for centuries, and why this bark gives colour on plant fibres that many other natural dyes struggle with.
Most natural dyes bond easily with wool and silk, which are protein fibres, but struggle with cotton and linen, which are cellulose. Tannin is the exception: it has a strong natural affinity for cellulose. That is why traditional cotton dyeing starts with a tannin bath before any other step. Because Mimosa tenuiflora root bark is itself rich in tannin, it supplies the dye and the tannin in one material.
On wool and silk the tannins and pigments attach to the protein directly, and an alum mordant gives them more sites to hold on to. The result is usually a deeper, redder shade than the same bath gives on cotton.
What you need
- Mimosa tenuiflora root bark: shredded, powder or whole
- Natural-fibre fabric or yarn (cotton, linen, wool or silk)
- A stainless steel or enamel pot used only for dyeing
- A strainer and a fine cloth
- Kitchen scales, a thermometer, gloves and a spoon kept for dye work
- Optional: alum as a mordant, and iron (ferrous sulfate) as a colour modifier
How much bark to use
Natural dyers measure dye as a percentage of the dry weight of the fibre (WOF). These are starting points; always dye a small sample first. Our dye quantity calculator works out the amount for any weight.
| Depth of shade | Bark, as % of dry fibre weight | Example for 200 g of fabric |
|---|---|---|
| Pale | about 25% | 50 g |
| Medium | about 50% | 100 g |
| Deep | about 100% | 200 g |
Water, pot and temperature
- Water volume: natural dye suppliers commonly work at about 30 parts water to 1 part fibre, so 3 litres for every 100 g. The fibre must be able to move freely or it will dye in patches.
- Water quality: soft water suits most natural dyes. Very hard water can dull or shift the shade; if your tap water is hard, try rainwater or filtered water for a test.
- Pot: use stainless steel or enamel. An iron or aluminium pot reacts with the tannin and changes the colour.
- Temperature: a gentle simmer, 80 to 90 °C, is enough. Hard boiling does not give more colour and tends to brown it.
Step by step
1. Scour the fabric
Wash cotton and linen in hot water with a little pH-neutral detergent. Dyers often add soda ash at about 1% of the fibre weight; Apple Oak Fibre Works describes the full method. Wash wool and silk gently in warm water with neutral detergent only, and avoid sudden changes of temperature. Rinse. This removes oils and factory finishes that stop dye from taking evenly. Keep the fabric wet.
2. Mordant if you want better fastness (optional)
Because the bark carries its own tannin, you can dye without a mordant. For stronger and longer-lasting colour, many dyers pre-treat fibre with alum. The amounts and method for each fibre are in the mordanting section below.
3. Make the dye bath
Put the bark in the pot and cover it with enough water for the fabric to move freely. If you are using whole bark, break it up and soak it overnight first. Heat to a gentle simmer, about 80 to 90 °C (175 to 195 °F), and hold it there for about an hour. Do not let it boil hard. The water should turn deep red-purple.
4. Strain
Pour the liquid through a strainer. With powder, line the strainer with a fine cloth, or simmer the powder inside a tied cloth bag from the start. Loose particles left in the bath can leave specks on the fabric.
5. Dye
Add the wet fabric to the strained bath. Keep it warm, just below a simmer, for 45 to 60 minutes and stir gently so the colour is even. For a deeper shade, turn off the heat and leave the fabric in the bath overnight.
6. Rinse and dry
Rinse in cool water until it runs nearly clear, then dry in the shade. Wait a few days before the first proper wash.
Mordanting in detail
A mordant is a metal salt that links dye to fibre. It is optional with this bark, but it improves how well the colour survives washing and light.
| Fibre | Mordant | Typical amount | How |
|---|---|---|---|
| Cotton, linen | Aluminium acetate | 5 to 10% of dry fibre weight | Dissolve in hot tap water, about 38 °C (100 °F), soak the fibre for 45 minutes |
| Wool, silk and other protein fibres | Alum (aluminium potassium sulfate) | 15 to 20% of dry fibre weight | Dissolve, add the wet fibre, raise the heat slowly to about 93 °C (200 °F) and hold for 45 minutes. Dyers usually keep silk a little cooler to protect its sheen |
These figures follow the mordanting instructions published by Dharma Trading. Always follow the instructions supplied with the mordant you buy.
Changing the colour
- Iron: a small amount of ferrous sulfate, around 1 to 2% of the fibre weight, reacts with the tannins and darkens the colour toward grey-violet and charcoal. Use it sparingly on wool, because too much iron makes protein fibres brittle.
- Second baths: the same bark can usually be simmered again for a paler bath, which is useful for tonal sets.
- Fibre: wool and silk generally take deeper, richer shades than cotton and linen from the same bath.
What iron actually does
Iron reacts with tannins to form dark blue-black compounds. Woodworkers use the same reaction to turn tannin-rich wood black, and a 2023 paper in the Journal of Wood Science describes it in detail. In the dye pot, a small dose of ferrous sulfate turns the pink-purple of the bark toward grey-violet, and a larger dose toward charcoal. Because the reaction is strong, add iron in a separate bath, a little at a time, and rinse well afterwards.
Troubleshooting
| Problem | Likely cause | Fix |
|---|---|---|
| Colour is too pale | Too little bark, or too short a time in the bath | Use more bark, or leave the fibre in the cooling bath overnight |
| Patchy or streaky colour | Fibre not scoured, crowded pot, or added dry | Scour properly, use more water, always add the fibre wet and stir |
| Dark specks on the fabric | Loose powder or fibres left in the bath | Strain through a finer cloth, or simmer the bark in a tied bag |
| Colour is brown instead of pink-purple | Bath boiled hard, hard water, or a reactive pot | Keep to a gentle simmer, test with soft water, use stainless steel |
| Wool feels harsh or has felted | Sudden temperature change, agitation, or too much iron | Heat and cool slowly, stir gently, cut the iron to 1% or less |
| Colour washes out | No mordant, or washed too soon or too hot | Mordant next time, wait a few days before washing, wash cool |
Caring for dyed fabric
Wash by hand or on a cool, gentle cycle with pH-neutral soap, and dry out of direct sun. Like all natural dyes, the colour will soften with repeated washing and strong light.
Keep a dye record
Results vary with fibre, water and the bark itself, so the most useful habit is to write down the fibre weight, the amount of bark, the time and temperature, and to keep a small swatch from every bath. For the quantities, the dye quantity calculator and the project planner will do the arithmetic and give you a sheet to print.
Safety
- Keep dye pots and utensils separate from cooking equipment.
- Wear a dust mask when handling powder, and gloves when handling the bath or iron.
- Work in a ventilated room and store mordants and modifiers out of reach of children and pets.
Frequently asked questions
Which form of bark is best for dyeing?
Shredded bark is the easiest all-rounder because it releases colour quickly and strains out cleanly. Powder is fastest but needs a fine filter. Whole bark needs an overnight soak. See whole vs shredded vs powdered root bark.
Can I dye synthetic fabric?
No. Polyester, nylon and acrylic do not take natural dyes well. Use natural fibres.
Do I have to use a mordant?
No. The bark is a tannin dye and will colour fibre on its own, but an alum mordant usually improves wash and light fastness.
How long does the whole process take?
Allow about three hours: scouring, an hour to make the dye bath, and 45 to 60 minutes of dyeing. Mordanting adds roughly another hour, and leaving the fabric in the cooling bath overnight gives a deeper shade.
Can I reuse the dye bath?
Yes. The used bath, or the same bark simmered a second time, gives a paler shade. Dyers use these second baths to make matching light and dark tones.
Sources
- Revista Árvore (2022): condensed tannin content of Mimosa tenuiflora bark
- Dharma Trading: fibre preparation and mordanting
- Journal of Wood Science (2023): the iron and tannin reaction
- Apple Oak Fibre Works: scouring and mordanting cotton and linen
Mimosa Tenuiflora Root sells root bark as a raw material for dyeing, soap making and cosmetic crafting only. It is not sold for human consumption.