Hydrosulfite Indigo Vat Recipe by Elisabeth Culshaw

A guest recipe by natural dyer Elisabeth Culshaw.

I am a natural dyer and I love working with indigo. It is such a special dye, and one has to feel grateful for it: it takes so much time, patience and energy to produce 1 kg of indigo. The indigo vat is a very special dye pot that creates beautiful blues.

I always work with natural indigo, and I love the strong blues I get with themazi's natural indigo extract. Not all indigo is equal: the purity of your indigo powder helps you get a fast, strong reduction in your vat.

Which indigo vat should you use?

In my studio I run a very large fructose vat for light blues and for wool, and an iron (ferrous) vat, which is perfect for dark colors on cellulose fibers. To give strong blues to wool, a hydrosulfite vat is perfect. It is also a great way to start working with indigo, because it is quick to prepare and the result is reliable, which makes it ideal for a short-term project. My favorite recipe is below. For a fructose vat and more on how indigo works, see themazi's indigo vat guide.

Hydrosulfite indigo vat recipe (10 liters)

You will need

• A non-reactive dye pot with a lid, and a 2-liter glass jar
• 10 liters of hot water (50 °C / 120 °F)
• 50 g natural indigo powder
• A mortar and pestle to make the indigo paste
• 60 g soda ash
• 15–20 g of a reducing agent: sodium hydrosulfite (sodium dithionite) or thiourea dioxide (sold as Spectralite)
• A spoon, pH paper, gloves
• Strips of cotton to test the color, such as our cotton gauze for dye testing

Step by step

1. Pour 8 liters of the hot water into the dye pot. Keep the other 2 liters in the glass jar to make a stock solution; a small "mini vat" is easier to reduce than the whole 10 liters.
2. Put the indigo powder in the mortar and add water little by little, grinding it into a smooth paste.
3. Add the paste to the glass jar, which should be about half full of water, and stir in a circle to distribute it well.
4. Dissolve the soda ash in a little water in a separate jar, then add it to the indigo jar.
5. Stir well. When everything is mixed, sprinkle the reducing agent on top. Stir gently clockwise, then counterclockwise.
6. Cover the jar loosely, not tightly, because some gas needs to escape during the reduction.
7. After about an hour the liquid should turn green, with blue bubbles on top. Stir again gently for a few minutes, right down to the bottom.
8. Leave it to rest for at least 5–6 hours. You should then see a dark yellow-green liquid with a coppery, blue iridescent film and bubbles on top, called the "flower".
9. Check the pH: it should be around 11.
10. The next day, gently pour the stock solution into the large dye pot of hot water. Stir slowly without splashing, and let it rest.

Your vat is now ready. Dip wet, scoured fabric for a few minutes without splashing, lift it out and watch it turn from green to blue in the air. Repeat for darker blues.

Learn with Elisabeth

Working with nature is very rewarding. I teach several processes online, including eco printing, natural dyeing and how to set up a natural indigo vat. You can find my online classes here.

Related: Shop natural indigo · Indigo vat guide with 3 blue shades · Natural tie-dye with indigo