Dyeing yarn with indigo

Indigo dye vats have fascinated me for a while now; the magic that happens when you add fibre to a yellow green dye pot to get a blue result puzzles and excites me. Recently I found the time (and courage) to have a go at it; thank you Sandy for the push.
First I did a fair bit of research about how indigo is made from the plant. Indigo is made from the leaves of indigo plants which are fermented, soaked in a caustic solution and then dried to produce the blue 'rocks' or powder that comes in the mail for me to play with.
Once I had my little pots of powders and chemicals, I downloaded the instructions for use and got to work...

I decided to dye some hand spun cotton as I had an order for cotton gloves.

I gathered up pots, scales, utensils, indigo, caustic soda
sodium hydrosulphite, yarn and a sense of adventure as per instructions 

I added the caustic and hydrosulphite to the 15 litres of water

I added the indigo to the dye pot

It made a big pot of blue at first, so I put the lid on and waited.

Until the pot was yellow/green with a copper scum on top.
This photo doesn't show the copper scum to full effect, but it is there.

I decided to experiment with cotton, merino and suffolk yarns (because I had those lying around).

Better late than never, I found a pair of rubber gloves.

I made a tiny skein to test dye first, this one is cotton.

Well, it came out blue.

So I tied the skeins to a bit of wood and lowered them into the pot.

They went a lovely shade of dog vomit green/yellow at first.
 The copper scum shows up much better in this photo.

I lifted the yarn out and waited for it to turn blue

Which it did

Then faded to a much lighter blue as it dried.

That was the batch that worked......the story of the vat that didn't is much the same until the 'lifting the yarn out' stage then I found that my four skeins of cotton yarn (which take forever to prepare and spin) had turned into a big blue jelly fish in the bottom of the vat. I eventually figured out that the 150g of caustic recommended in the instructions was just too much for the yarn and it melted. The second lot I cut the caustic down to 15g (about a tablespoon) and it worked well; must have been a misprint.

In ancient times indigo dye vats were made using stale urine (because they didn't waste anything). The processed indigo was stuffed into a cloth bag and lowered into a big tub of stale urine and left to ferment for a week. Cloth and fibre was then soaked in the vat for various lengths of time then rinsed (really well, I would think) and left to dry in a breezy place. This kind of dyeing vat is called a sig vat. I will try this method at some point, when I can afford more indigo dye.
Maybe I should try growing some indigo plants, what do you think?
Have you tried indigo dyeing? What was your experience?