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Bluivance. Plant indigo, dyed by hand in Porto.

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The Bluivance seal, an indigo stamp holding a b over 2016b2016

Three vats. All of them alive.

This is the part I could talk about all day. Indigo will not dissolve in plain water, so every vat here is a small living thing that has to be fed, warmed and watched before it will dye a single skein. Here is how I keep them.

Inês

Velha, Rio and Pequena

The 2019 vat

Velha, the old vat

200 litres. A bran and madder fermentation vat started on 14 March 2019, the week the studio moved in, and still dyeing every week. It gives the softest, most even blues we make, and most of the yarn.

The 2022 vat

Rio

200 litres. A fructose and lime vat made up in 2022, quicker to recover after a heavy day of dipping. Most of the cloth goes through Rio, because long lengths tire a vat out.

Samples only

Pequena

60 litres, kept for sample cards. Five shades on 50 g never tire the big vats, and your card comes from the same kind of liquor as your order.

  • 200litresVelha
  • 200litresRio
  • 60litresPequena
  • pH11Held with lime
  • 30°CThrough winter
  • 12dipsFor Noite
Velha, drawn in section A 200 litre vat with a skein hanging from a dowel into the liquor, the coppery flower floating on top, bran and madder settled on the bottom and an immersion heater down one side. 1234
  1. The flower, coppery and bubbled, the vat's own report on how ready it is.
  2. The liquor, yellow green below the surface, near 30 °C and pH 11.
  3. Bran and madder on the bottom, feeding the bacteria that keep the blue in solution.
  4. The immersion heater, in from November to April.

Keeping the vats

A fermentation vat is closer to a sourdough than to a bucket of dye. Indigo only dissolves once the oxygen has been taken out of the water, and in Velha that work is done by bacteria living on the bran. Keep them fed, warm and alkaline, and they keep the blue in solution. Neglect them for a fortnight and you have two hundred litres of brown water and a long week ahead of you.

Bran every five days

Velha gets a scoop of wheat bran every five days, stirred in gently at the end of the afternoon so the sediment has the night to settle. With it goes a handful of madder root, chopped small. Madder is a dye in its own right, but in this vat it never colours anything; it feeds the fermentation and seems to make the whole vat steadier. Rio is simpler. A measure of fructose when it starts to tire, and it is back at work the next morning.

Lime, and holding pH 11

Both big vats need lime to hold at about pH 11. Below ten Velha's bacteria get lazy and Rio's fructose stops doing its work, and the indigo begins to drop out; much above eleven and a half and wool and silk start to suffer. I test every morning before the first dip and add lime a spoonful at a time, never a cupful. After all these years I can usually guess from the way the liquor runs off the stirring stick, but I still check with the paper.

Warmth through a Porto winter

Velha's bacteria are happiest near 30 °C, and Rio reduces faster when it is warm too. A Porto winter is nothing like 30 °C. From November to April an immersion heater sits in each of the big vats. The cold is not really the enemy, though; the damp is. Wet Atlantic air pulls the warmth out of everything it touches, so on the worst weeks the vats wear old wool blankets and the lids stay on overnight.

Reading the flower

Every morning there is a skin on each vat, and in the middle of it a cluster of coppery, bronze bubbles we call the flower. It is the best report a vat can give. A thick flower that shines like a new coin means the vat is well reduced and ready. A thin, dull one means it is hungry. A blue skin and no flower at all means too much air has got in, and the dipping waits for the afternoon. I lift the flower aside before I dip and lay it back afterwards, so the vat keeps its lid.

August, and why the vats rest

In August the workshop warms up on its own and the vats ferment faster than I can use them. Velha develops a smell the neighbours are very polite about: sweet, earthy, a little like a farmyard after rain. It means the bacteria are thriving, not that anything is wrong. But a vat worked every week of the year benefits from a pause, and so do I. From 1 to 15 August the lids go on, feeding drops to once a week, and nobody dips anything.

A single dip, step by step

  1. The fibre is wetted right through first, so the dye goes in evenly and not in patches.
  2. It is lowered under the flower slowly, without dragging air in, and held there for ten minutes.
  3. It comes up yellow green. That is the indigo still dissolved, before it has met the air.
  4. It hangs for twenty minutes, and the green turns to blue while you watch.
  5. Back in. Two dips for Névoa, five for Ribeira, ten to twelve for Noite.

Patience, not strength

You could make a much stronger vat and reach Noite in three dips. It would look dark for a week and then rub off on every hand that touched it. Each dip leaves a thin layer that settles into the fibre as it turns blue, so a deep shade built from twelve thin coats does not rub off. That is the whole reason Noite adds a week.

Where the indigo comes from

Every vat here runs on plant indigo powder, bought by the kilo from small growers of Indigofera in India and Central America. It arrives as a dark blue dust that smells faintly of hay, and it is the only colour that ever goes into a vat at Bluivance. No synthetic indigo goes in, and no pre-reduced indigo either, even when a customer offers to bring their own. You can see the difference on the card: plant indigo keeps a little of the leaf in it, and its deep shades carry a warmth the synthetic kind never quite has.

Where next

  • Dyeing and pricesWhat each shade costs on yarn, cloth and garments, and what we turn away.
  • The studio and InêsThe garage, the workshop and skeins drying on the stairwell rail.
  • Write to usTell us your fibre and your shade, and we answer within two working days.