Urine Vat (or Sig Vat)
The urine vat has a strong smell and is best used outside during the summer.
Collect enough urine to fill a five litre container. Any urine will do, but make sure you store it in a well-marked container and keep the lid on. Place the container in a warm place. A greenhouse is a possibility, providing it does not get too hot inside.
Add three teaspoons of woad powder to the bucket with the stale urine. In a few days the vat should change in colour from blue to greenish yellow.
Add well-washed wet fibre to the bucket and leave it for an hour or longer. Air the fibre and keep re-dipping it in the vat until the fibre is the shade of blue that is required. Keep the vat topped up with urine and add more woad when necessary.
Liles’s book mentions five reasons to learn to use a urine vat (see also his web excerpt).
- you can get some shades only with a fermentation vat
- the fibre can be left in the vat up to two days, producing a more permanent colour.
- once working, the vat needs little attention
- it is easier to build darker colours
- the satisfaction of reproducing a method used for thousands of years
See also the Chemical method