I have now experimented with a stronger vat, this time using 2 teaspoons indigo, 4 teaspoons calcium hydroxide and 6 teaspoons fructose – that is, double the quantities used in my first vat.
I dyed the same quantities of fibres following the same methods but the depth of blue I achieved was no deeper than from the first, weaker, vat. This would indicate that this vat gives pale to mid blues but not the deep blues which other indigo dyeing methods give. I wonder whether this vat may be best used for patterning fabrics employing resist techniques, rather than for dyeing skeins of fibre as I tend mainly to do. I also noticed that this vat left the wool feeling rather harsh. However, I didn’t use a vinegar after-bath, which might have been advisable to counteract the effects of the strong alkalinity of this vat. (I never usually use a vinegar after-bath, so I’m afraid it didn’t occur to me to do so after this vat.)
If anyone else has any comments to add on using this type of indigo vat, I’d be delighted to receive them.