Monday, 30 May 2011

Michel Garcia vat

This vat has been a puzzle since La Rochelle but I have clarified the oyster shell component with Michel, who explained that in order to use the shells, they need to be heated to 1,000deg C. He has a pottery kiln, so this is not a problem for him. He suggested I use calcium hydroxide
This afternoon I made the vat according to Garcia (his proportions, my quantities):

1 teaspoon of indigo - I used Pure Tinctoria powdered extract

2 teaspooons of calcium hydroxide

3 teaspoons of fructose

The teaspoons were level and the vat is a large Kilner Jar.

The pH was 11, as recommended by Garcia

Within 10 minutes the vat had gone from grey through green to yellow

By 25 minutes, there was blue foam forming on the top and a coppery scum developing - much like my rising levels of excitement!

After 30 minutes the foam had turned dark blue

Left: Vat at 25 mins, Right at 45 mins containing cotton
At 45 minutes, the vat should be ready, according to the instructions. The pH was still 11 and remained at that level throughout the dye session.
I put in a cotton wool ball and a piece of cotton in the vat which now had the sherry colour that one expects from woad

The first dip, airing

The second dip for cotton (large piece) and first for linen

Third dip for cotton and second for linen

All in all, very successful and the vat is by no means exhausted, so I will go on until one of us gives up! What I'm not sure about is how to revive such a vat - there's no problem with reviving more usual vats. I warm them up, correct the alkalinity and put some reducing agent in and they come round. This will need some experimentation, I think


  1. Brilliant, Jane. It's the first thing I want to do when we move. No time at the moment.

  2. I read through this several times, but didn't see any temps you used? apparently the vat seems to be temperature-sensitive (at least from what I read in other blogs...) - could you clarify please? thanks - and happy dyeing from the west of ireland:)

  3. Well, Michel said that he started the vat at 80 C and we all thought that sounded a bit warm, but on reflection I wonder if it is to melt the fructose?

    So I started mine hot - not sure about the exact temperature but hotter than I would usually have a vat - and it went on working even when it had cooled down significantly. It continues to work when warmed up slightly but I have reservations about the fastness of the colour. It wasn't very lightfast in my conservatory.