Indigo Fructose Dye Vat

By Paivi Suomi on February 25, 2017

There are many ways to prepare an indigo vat, some use soda ash and spectralite, some use some use sulphuric acid, some use iron and some urine. For this indigo vat, I am using a fructose base. You can also use ageing fruit instead of fructose sugar.

The fructose indigo vat was developed by Michel Garcia. The addition of the fructose sugar acts as a reducing agent to the Indigo. The sugar removes one of the oxygen molecules from the indigo making it soluble in water.
The addition of the Calcium Hydroxide (slaked or hydrated lime) changes the pH from an acid to a base. The proper pH to get good colour on wool should be about +9 and for cotton and cellulose +10.

When the yarn or fabric is dipped into the indigo dye vat, it turns a green colour. When the yarn is raised into the air, the oxygen molecules from the air, bind with the indigo and turn the green into blue. To get darker and more intense blues, the yarn needs to be dipped into the indigo vat and raised into the air to oxidize several times. The colour builds up onto the yarn or cloth in layers. Keep dipping and airing out the yarn until the desired level of colour is achieved.

An Indigo vat can be re-used and kept alive for several weeks until all of the indigo has been exhausted.
If the Vat still has indigo but has turned blue, reheat the Vat to 50 deg C. Check the pH. Add about a teaspoon of fructose crystals and wait 15-30 minutes.
The Vat should turn green. If it is still blue add some Calcium Hydroxide. pH should be +9 for wool, or +10 for cellulose.

The Fructose Indigo Vat uses a 1-2-3 ratio of substances.
1 part Indigo
2 parts Calcium Hydroxide
3 parts Fructose

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I purchased some Tamil Nadu Indigo from Wild Colours.
I decided to make a starter indigo vat using 25 grams of Indigo. In theory, 25 grams of Indigo will dye about 1 kg of fibre. This will vary depending on the strength and depth of colour that you produce, and the Vat can be kept alive by checking pH and adding more Calcium Hydroxide or Fructose as needed.

I put about 200 ml of hot water into a large Kilner jar and added the Indigo powder. I stirred this until the indigo was dissolved.

Indigo Fructose Dye Starter Vat

I then added more warm water to fill the jar almost to the top.

I measured out 50 grams of Calcium Hydroxide
and 75 grams of Fructose.

Indigo Fructose Dye Vat

I added the Fructose into the Indigo mixture and stirred until it was dissolved.
Then I slowly added about half of the Calcium Hydroxide, trying not to introduce air bubbles into the mix.

The Indigo starter needs to be kept warm while it reacts, so I placed the Kilner jar into a slow cooker filled with warm water. I left it on a low setting and gently stirred the jar about every 20-30 minutes.

Indigo Fructose Dye Vat

After about 3 hours, a bronze film had developed on top of the water, and the indigo bath had turned green.

Indigo Fructose Vat

Indigo Fructose Dye Vat

I let this starter vat sit overnight and kept it warm by wrapping a towel around it.

The following day the Indigo starter had separated into several lovely layers.

Indigo Vat Layers

I put 10 litres of hot tap water (50 Deg Celcius) into a large plastic pail.
I carefully lowered and submerged the jar of Indigo starter into the pail. I gently tipped the jar to pour out the indigo taking care not to introduce extra air into the water.

Indigo Fructose Vat

I gave the Vat a gentle stir and let it sit beside the warm radiator. More patient waiting…

A few hours later:
Indigo Fructose Vat: pH +11.2 Temp 30 deg C.
The Indigo Vat looked like it was ready to go.
A coppery finish had formed across the top and the dye water looked green.

I tested a few wool yarn samples and dipped them into the Vat. They came out green, but quickly turned to blue in the air.

Indigo Fructose Dye Vat Sample No. 1
For my first real test piece I dipped in a skein of handspun bleached flax. I dipped the skein into the Vat, pulling it out after about a minute and let it air for about a minute. I repeated the dipping 5 times and got quite a dark blue that I was happy with.

Handspun Flax
60 gram skein 160 m
approx. 260 m/100 gr

Handspun Bleached Flax

Handspun Flax in Indigo Vat

Indigo Fructose Vat Dye Sample No. 2

I tied a silk scarf with some marbles and elastics, creating a Shibori type of effect.
I dipped the scarf (dry) into the Vat, swirled it around and pulled it out to air for about a minute. I repeated the dipping 5 times.

Silk Scarf dyed with Indigo

First set of samples drying outside.

Flax and Silk dyed with Indigo

After you have finished dyeing your pieces, rinse them thoroughly in cold water until the water runs clear. Add a bit of vinegar to the final rinse, to neutralize the high pH of the yarn or fabric, as this can be damaging to your yarn if it is left.

Indigo Shibori Silk Scarf

Indigo Dyed Silk Scarf and Linen Yarn

I put a lid onto the Vat and have it placed near a radiator to help keep it warm. There is still LOTS of colour left in the Vat – I will try dyeing something else in a few days.