Guide til indigokar: sådan farver du med naturligt indigo (3 blå nuancer)

Indigo is not a regular dye bath. It is a vat dye: the indigo must be reduced (made soluble) to enter the fiber, and it turns blue again when it meets oxygen in the air. That is why indigo gives unmatched blues, and why beginners sometimes struggle. This guide explains how indigo works, how to build a simple vat with natural indigo extract, and how to dye three reliable shades: sky blue, classic indigo blue and deep navy.

What is natural indigo extract?

Natural indigo extract is indigo pigment made from the leaves of indigo plants, usually Indigofera tinctoria. Unlike most natural dyes, indigo does not need a mordant. Instead it attaches to the fiber through the vat process:

reduce → dye → oxidize → repeat

The key idea

• In the vat, oxygen is removed and the indigo becomes soluble and yellow-green, so it can enter the fiber.
• When you lift the fabric out, oxygen returns and the indigo turns blue and becomes fixed in the fiber.

Understand this, and you understand most of indigo dyeing.

Before you start

1. Choose your fiber

• Cotton and linen: crisp, classic indigo blues.
• Wool and silk: take indigo well, but need gentler handling and a less alkaline vat.

Our undyed cotton and linen fabrics and dye-ready blanks are ideal for indigo and shibori.

2. Scour the fiber

Oils and finishes cause patchy color, so always scour first. See how to prepare fabric for natural dyeing.

3. Know what a healthy vat looks like

• It is alkaline (pH about 10–11; a little lower for wool).
• It is reduced: the liquid under the surface is clear yellow-green, not blue.
• There is a coppery, bronze film and bubbles on top, called the flower.
• Fabric comes out yellow-green and turns blue in the air.

How to build an indigo vat

Every indigo vat needs three things: indigo, an alkali and a reducing agent. Dyers use different reducers:

• Fructose vat: uses fruit sugar as the reducer and slaked lime (calcium hydroxide) as the alkali. A popular natural, long-lasting vat.
• Hydrosulfite vat: uses sodium hydrosulfite or thiourea dioxide with soda ash. Fast and reliable, ideal for beginners and short projects. See our hydrosulfite vat recipe by Elisabeth Culshaw.
• Iron (ferrous) vat: uses iron and lime; good for dark blues on cotton and linen.

Fructose vat (1-2-3 vat)

This simple vat, popularized by Michel Garcia, uses the ratio 1 part indigo : 2 parts slaked lime : 3 parts fructose by weight. For example, 10 g indigo, 20 g lime and 30 g fructose in about 3 liters of water for medium blues. Use about 2 g of indigo per liter for light blues and 7–10 g per liter for navy.

1. Mix the indigo powder with a little warm water into a smooth paste.
2. Fill a pot or bucket with warm water (about 50 °C / 120 °F) and stir in the fructose until dissolved.
3. Add the indigo paste and stir.
4. Add the lime slowly, stirring gently in a circle.
5. Cover and leave for about an hour, stirring gently once or twice, until the liquid turns yellow-green and a flower forms on top.

Keep the vat warm for best results. If it turns blue, add a little more fructose; if it stops working, add a little more lime, then wait.

Vat logic (always the same)

1. Make the vat alkaline.
2. Reduce the indigo.
3. Dye with as little air as possible.
4. Oxidize the fabric in the air.
5. Repeat for depth.

3 indigo shade recipes

These recipes assume you have scoured your fabric, built a working vat, and are dyeing at room temperature to warm, never boiling. Depth in indigo comes from several short dips, not one long soak.

Recipe 1: Sky blue (1–2 dips)

1. Lower the wet fabric into the vat and keep it under the surface for 1–2 minutes, without splashing.
2. Squeeze it gently under the surface.
3. Lift it out and let it oxidize in the air for 10–15 minutes.
4. Rinse lightly after the final oxidation.

Too pale? Add one more short dip.

Recipe 2: Classic indigo blue (3–6 dips)

1. Do 3–6 short dips of 1–3 minutes each.
2. Let the fabric oxidize for 10–20 minutes between dips.
3. Let the color build gradually.

Recipe 3: Deep navy (6–12+ dips)

1. Repeat 6–12 or more dips, with full oxidation between each.
2. Keep the vat healthy: minimal air, stable alkalinity, good reduction.
3. Finish with a thorough rinse and gentle wash.

If the color stops getting darker, the vat needs to be rebalanced: add more reducer or alkali and let it rest.

Aftercare

• Rinse until the water runs almost clear.
• Wash gently with a pH-neutral soap after the final oxidation. A rinse in water with a little vinegar neutralizes the alkali.
• Dry away from strong direct sun.

Troubleshooting

The fabric does not come out yellow-green

The vat is not reduced enough, or not alkaline enough, so the indigo is not soluble.

The blue washes out quickly

The fabric was not scoured well, the dips were too long without oxidation, or the vat was not properly reduced.

The vat has turned blue

Too much oxygen got in. Let it rest covered and restore the reduction.

The color is patchy

Usually poor scouring, too much fabric in the vat, or splashing air into the vat.

Safety

Indigo vats are alkaline. Wear gloves and eye protection when handling lime and reducers, avoid splashing, and keep containers labeled and out of reach of children and pets.

Glossary

• Vat: the dye bath in which indigo is reduced.
• Reduction: removing oxygen so the indigo becomes soluble.
• Oxidation: the indigo turning blue again in the air.
• Flower: the coppery foam on the surface of a healthy vat.

Ready to dye?

Shop natural indigo extract and fructose, or browse natural blue dyes. For bulk orders, see our wholesale page. For overdyeing, try indigo with weld for greens.