This is my first attempt at starting and maintaining an indigo dye vat. I'm using the 1-2-3 method that was come up with by Michel Garcia using one part indigo, two parts calcium hydroxide, and three parts fructose. This looked like a good starter recipe for me because I could easily get the ingredients, it doesn't produce harmful fumes, and when I eventually want to dispose of it it can go down the drain (if you're using different ingredients in your natural dyeing, don't assume that they're harmless to you or your water system without researching first!). Most of my information comes from The Art and Science of Natural Dyes, by Joy Boutrup and Catharine Ellis. It's quite a pricey book, but contains a lot of really useful recipes and information.

I was aiming for two gradient sets of yarn, one dyed only with the indigo vat, and the other undergoing the same treatment, then 'saddening' and darkening the colours with ferrous sulphate. Overall I'm happy with this as a first attempt, but I'll be listing things I'd do differently/experiment with as well next time at the end of this instructable.

Supplies

yarn: I used 8x10g micro skeins of superwash sock yarn, composed of 75% merino 25% nylon. Superwash means it shouldn't felt when you're dyeing or applying heat
20g natural indigo pigment (plus more for future vat maintenance)
40g calcium hydroxide (plus more for future vat maintenance)
60g fructose (plus more for future vat maintenance)
mortar and pestle, or a plastic jar filled with marbles/smooth stones
lidded plastic or stainless steel bucket (tall and narrow works best)
old broom handle or other large stirring stick
plastic or stainless steel bowls you're happy never to use for food
stainless steel saucepan, also never to be used for food
string
mesh laundry bag
white vinegar or citric acid
neutral detergent (I used synthrapol)
optional: ferrous sulphate
optional: sodium acetate

Step 1: Prepare Indigo

Weigh out your indigo, and add it to either your plastic jar with marbles or your mortar and pestle. Add some hot water, then shake the jar or grind it into a paste in your mortar and pestle. Then separately dissolve 60g of fructose in boiling water.

Step 2: Make Vat

Add around 6l of almost boiling water to your bucket, then stir in the fructose solution. Add the indigo paste and stir again. Add 40g of calcium hydroxide next, stir again. Add some more hot water, bringing it up to around 10l. Stir carefully using a circular motion, aiming to introduce as little oxygen as possible into the vat. Cover, and continue to stir once an hour for several more hours. I then left it overnight to reduce (the aim of an indigo vat is to remove the oxygen from the liquid, so the dye will become soluble).

Step 3: Check Vat

The next day, your vat should have some foam and a metallic sheen to the surface. The liquid should be a dirty yellowish colour. I checked the pH of my vat (9 is perfect for wool, but for dyeing cellulose fibres like cotton you want it higher), and covered it again while I prepared my yarn for dyeing.

Step 4: Prepare Yarn

Yarn wound into a skein is perfect for dyeing. If your yarn is in a ball or on a cone, you'll want to wind it round something (a niddy noddy is the traditional tool, but you can also use a large hardback book or similar), and tie it with multiple loose figure of eight knots to keep the strands together. I also loosely tied my skeins together in pairs, because I wanted two of each shade. Soak your yarn for around half an hour in warm water.

Step 5: Prepare Dye Bag

I decided to suspend my skeins in a mesh bag, to prevent them from touching the bottom (as you use the vat, sediment will build up at the bottom, and inhibit even dyeing), so I tied the bag to some string, and attached it to the handle to dangle in the vat.

Step 6: Add Yarn

Squeeze the water out of your yarn, and add it to the mesh bag. Lower it gently into the vat, introducing as little oxygen as you can. Once it's below the surface, give it a few more squeezes to let the dye penetrate more easily. Cover the vat and leave for fifteen minutes.

Step 7: Oxygenate Yarn

After the fifteen minutes are up, squeeze the yarn under the surface, before removing it from the vat. Squeeze out the remainder of the liquid into a separate jug (not the vat), so you don't add oxygen to the vat. Put the lid back on the vat again. Then rinse the yarn in cold water, and hang it somewhere to oxygenate for forty five minutes. The yarn should turn from a greenish colour to blue.

Step 8: Repeat Steps 6 and 7

Continue dipping your skeins for fifteen minutes, and oxygenating them for forty five. I did four shades of blue, for two, four, six and eight dips each, spread across two days. As I didn't want the alkaline pH to damage the yarn, I followed step 10 twice, once at the end of each dyeing day.

Step 9: Feed Vat

Once you're done dyeing for the day, dissolve a bit of fructose in boiling water (I did about a tablespoon of fructose - how much you use depends on how much dyeing you did), and add it to the vat along with any liquid you squeezed out and reserved. Stir the vat thoroughly, put the lid on and put it somewhere out of the way.

Step 10: Neutralise and Finish Yarn

To neutralise the pH of the yarn, soak it in a bath of 15ml white vinegar to 1l water, or half a teaspoon of citric acid and 1l water (whichever you have to hand) for at least fifteen minutes. Then in a stainless steel pan simmer the yarn and a good amount of water at 80 degrees for ten minutes. Allow the yarn to cool, then soak in a little detergent and rinse.

Step 11: Drying the Yarn

While the yarn is still in its rinsing water, untangle any strands that have got caught up. It's far easier to untangle them wet than leaving them to dry. Then, squeeze out the water from each skein, and put both hands inside the loop of the skein. Snap your hands apart quite strongly (this helps align the fibres, again reducing tangles). Put the skeins on a tea towel, roll it up, and squeeze out any water left. Then hang them to dry on a rack.

Step 12: Iron Dyeing

This stage didn't produce as much change as I'd hoped, but I'm including it anyway with some thoughts on what to do differently next time.

I weighed out 0.8g ferrous sulphate and 0.8g sodium acetate and dissolved them in a bowl of warm water. I then added half the yarn (one skein of each of the four shades), and left it for ten minutes. The colour changed a little, but I was hoping for a darker shade. I then tried simmering the yarn in water and 1g ferrous sulphate, which worked a little better. Next time I will try 1.5g of ferrous sulphate and sodium acetate, and put that mixture on the hob.

I then rinsed and dried the yarn using the same process as before.

Step 13: End Results and Future Thoughts

Once the yarn was all dried, I retwisted the skeins for storage. The first picture shows the four skeins dyed solely with indigo, and the second picture shows the same shades treated with iron afterwards. The third picture is each pure indigo and saddened iron shade side by side.

Overall, I'm happy with this as a first attempt. Next time I dye with indigo, I'll try: doubling the size of the vat, which should help with evening out the dyeing; dyeing to deeper shades (the two darkest shades show less difference than the ligher ones, I think because of the reduced amount of remaining indigo. Next time I'll try more dipping, e.g. 2, 4, 7, 11 dips rather than 2, 4, 6, 8); playing more with the iron dyeing, and also overdyeing with madder, cochineal or weld to get purples and greens as well. I will also be trying some traditional silk shibori, once I have a better handle on dyeing with wool.

I'm also interested in trying a naturally fermented vat using fruit rather than fructose (the fructose vat works well, but is apparently harder to maintain than a fermentation vat for longer term usage), and making the iron solution myself from rusty nails or wire wool.