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1. Harvesting Japanese indigo leaves
2. Steeping Japanese indigo leaves
3. Straining the liquid
4. Adding soda ash
5. Aerating the indigo vat
6. Settling out Japanese indigo Pigment
7. Concentrating Japanese indigo Pigment
8. Drying Japanese indigo Pigment
9. Dyeing with Japanese Indigo (opens new page)
Follow the usual precautions of wearing rubber gloves and a face mask when handling chemicals.
1. Harvesting Japanese Indigo leaves
July and August are the best months for harvesting Japanese Indigo in the UK. I usually harvest about a kilogram of leaves and stems. Wash them well under the tap then wash them again by dipping and shaking a handful at a time in a bucket full of water. There is no need to remove the stems or to tear up the leaves. Proceed to the next step as soon as possible to avoid the loss of pigment.
2. Steeping Japanese Indigo leaves
Put a 10 litre stainless steel saucepan inside a sink. Cram the Japanese indigo inside the saucepan. If you are short of space in your pot you can remove the stems. Fill the saucepan to the top with hot tap water (my tap water is at about 50 °C) and put a lid on. Fill the sink half full with hot tap water. Leave the saucepan for 24 hours. I replace the hot tap water in the sink three times in the 24 hours, but I am not sure whether this is really necessary.
3. Straining the liquid
After 24 hours, there should be some blue in the saucepan. Put a colander over a bucket and then strain the liquid through the colander. Pour the liquid back into the saucepan leaving any debris behind in the bucket. The spent leaves can then go on the compost.
4. Adding soda ash
Fill a mug-size container with boiling water and add 3 teaspoons of soda ash (it produces less froth than washing soda), dissolve well and let it cool slightly before adding it to the saucepan. Test the pH with a strip of pH paper. The pH should be 9, if not add another teaspoon of soda ash. I found that Japanese indigo usually needs an extra teaspoon of soda ash to reach pH 9.
5. Aerating the indigo vat
The indigo extraction vat now needs to be aerated to precipitate the pigment. To aerate the vat, whisk for 10 to 15 min with an electric whisk, until the froth turns blue and then green again. This can be done with a manual whisk but it will take longer. Some people pour the liquid from one saucepan to another but this takes even longer.
You now have the choice of either settling the indigo pigment or using the extraction vat itself together with spectralite. I recommend this second approach, using the extraction liquor, rather than trying to settle the pigment.
Click here to go to dyeing with the extraction liquor directly.
6. Settling out Japanese Indigo Pigment
Japanese indigo pigment is difficult to settle, and even when it does, a lot of blue pigment is left behind and wasted. Let the pigment settle undisturbed for at least three days. Using a soup ladle, very gently transfer a third of the liquid from the top of the pan into a bucket. This liquid you will throwing away will probably be bright blue. Pour the remaining liquid into large coffee jars with the help of a funnel. Put the jars in the shade and let the sediment settle for at least another three days. Every time you disturb the pigment it needs a long time to settle.
Gently tip the liquid from the top of each jar into a bucket, leaving the last 6 cm of liquid in each jar. Use a large pipette (for example, a glass siphon sold as a turkey baster in kitchen shops) to siphon liquid from the top of the jar. The pipette allows me to remove most of the unwanted liquid with little disturbance to the pigment in the bottom of the jar. (Pipettes sold in wine making shops are often not very useful, as they are designed to remove pigment from the bottom of a container, rather than skim liquid from the top). Consolidate the contents of the jars into one jar.
7. Concentrating Japanese Indigo Pigment
Let the liquid in the jar settle for another three days. You might see a blue sludge at the bottom of the jar. Carefully empty 2/3 of the jar or siphon most of liquid away with a glass siphon. Then fill it again with clean water. Repeat two or three times more until there is clear water over blue sediment.
8. Drying Japanese Indigo Pigment
The indigo dye pigment can now be dried for more permanent storage. Siphon away as much water as possible from the glass jar, and then empty the contents of the jar into an old Teflon saucepan or frying pan; an old ceramic plate can also be used. After a few days the indigo dries up and peels easily from the saucepan. It helps if you keep the saucepan somewhere warm, such as near a radiator. Do not put it in the oven, as it will get too hot.
9. Dyeing with Japanese Indigo (opens new page)
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