Sunday, 6 May 2012

Finishing Up a Hydro-sulphate Indigo Vat

The chalk-like sediment is visible when you stir the indigo adding to the guesswork of the condition of the vat.
A hydro-sulphate de-oxidised indigo vat cannot last forever. The slaked lime (or other alkaline agent) and the exhausted hydro-sulphate eventually build up at the bottom of the vat. When the vat is stirred the liquid in the vat becomes cloudy from the disturbed sediment. This adds one more factor to consider when reading the condition of the vat each day. It takes time after each agitation (intentional or accidental) to settle to the bottom again and then it is lurking there and going to effect the quality of the dyeing by getting on thread etc. When the thread dries a white powder can form. This could be the result of suspended sediment in the dye liquid.

It is not desirable to make a new vat every few weeks because there will be a reasonable amount of precious indigo pigment thrown away with the water as well as being a lot of work.  When you stir the indigo and feel the sludge at the bottom of the vat building up, imagine what is happening down there in the deep blue.  The above mentioned whitish-green cloud in the freshly stirred indigo is also an indicator that  it is time to go through the hassle of cleaning up the vat and starting fresh.

Of course the vat will have usable indigo pigment in it. The trick is how to exhaust the pigment effectively and properly.

There was no denying yesterday that the ceramic vat outside the front door needed re-done. Liza dropped in a piece she was dying. It floated to the bottom and when I retrieved it it was covered in deep-sea indigo monster mucus.

There were three more kilograms of red cotton thread to over-dye with indigo sitting there. They were put in the bath tub after the humans were finished last night and this morning they were well wet enough to dye. The indigo vat in question got a good spiffy up with a topping off of water, the pH adjusted and a good hit of hydro-sulphate and a strong whirlpool stir  before bed. The sediment had all settled by morning and the thread was dyed gently five times until it was obvious the pigment was nearly all soaked up.

Thank you indigo vat. I set this one up with Eri chan one cool November morning a year and a half ago. It had been very well used.

I threw in an old Snoopy blanket to suck up as much pH as possible and then hung that in the sun to dry. It will get thrown away with the regular garbage and they can burn it with the filter at the garbage dump. The exhausted dye bath was drained onto the gravel near the stream. Not strictly the most environmental thing to do but I worry that the sudden pH shock will kill the bacteria in the new state-of-the-art septic tank that was just installed.

Ryoma and Ryota were over for a visit and nothing could keep these curious little handsome weasels away from the main event of the sludge coming out of a hose. Of courser their white t-shirts ended up dyed blue.

The sludge at the bottom of the vat was scooped out and spread thin on a piece of plywood to dry in the sun.  That will take a few days and then it will be scraped up and put in a plastic bag and thrown away in the regular garbage.

The work involved in keeping a indigo vat going over a long period of time is daunting whether it is a fermentation vat, a hydro-sulphate vat or a zinc vat. (Jean I think of you!) Any questions just ask.

Bamse kept a distance but was caught up in the general vat emptying excitement. On a windy spring morning the most mundane things are amplified and bigger than life.


  1. how do you heat the vat in the ceramic vessel? I get the best results when I re-heat the vats (be it organic or chem reduction, exception is my fermentation vat which exists and dyes at very low temperatures) before dyeing. But this always means, I need a vessel that can be heated in some way. So when I read of your ceramic vessel at the front door, I was wondering.

    1. Ulrike san:
      it is not necessary to heat a hydro-sulphate vat. I have used one in almost freezing conditions for almost twenty years. I put in a large fish tank heater in a closed off tube when I am dying a lot of material in the winter. I do this to keep my hands warm more than effecting the condition of the dying. Cold indigo does not dye wool very well that is for certain. I use a fermentation vat only in the summer because keeping the temperature steady was troublesome with an above the ground vat.

      I wonder when I read about keeping a hydro-sulphate vat warm. The indigo particles do stick together in colder weather but a good stir usually keeps the vat in usable condition.

  2. Farewell (less than) sweet indigo vat.

  3. thank you for the tips.what to do with the remains has always stressed me out.