Here is a blog post on how to extract blue dye from Japanese Indigo. Recently I have been growing Japanese indigo at home. The purpose is just solely for fabric dyeing. Japanese indigo has been around for centuries. Japanese indigo is also known as Pesticaria tinctoria. I have previously been growing woad as well as using bought indigo. There is nothing wrong with using shop-bought indigo. However, I found it expensive in a long run. Now I would like to grow my own indigo dye. Also at least I will know the source of the indigo I use and that it is grown organically and ethically.
I must say that I am no professional dyer but a self taught one. I have read a few books written on it and caught the passion since.
How to extract blue dye from Japanese indigo.
There two ways to extract blue dye so far I have used one method. The degree of blue dye obtain from Japanese indigo depends on the variety of Japanese indigo. As far as I know, there are three types. They each yield different degrees of blue once extracted. I am using the sharp narrow pointed leaves variety. It produces pale pink flowers. This variety is easy to grow in a temperate climate like the UK. However, the variety I got yields the palest blue. At least it will be good to make green dye with Weld.
To extract I just soak the harvested leaves in hot boiling water. Don’t boil the leaves as it will overcook them and it will produce brown beige color instead. Leave the soaked leaves steep at least overnight and a few more days. If the weather is warm like in the summer no need to use boiling water. Leave it for a few days. This step is a unique step specifically to extract blue dye from Japanese indigo. It’s called the fermentation process. Then once you see some blue dye a few days later then it will get a strong fermented smell. It’s ready but this readiness is debatable.
Getting blue dye powder
Normally I would use straight away like the next step below. But I believe one can let the blue settle to the bottom and let it dry. It becomes a powder. Some use Pickling Lime or Calcium Hydroxide food grade to let it settle quickly. Be warned though as one kilo of harvested leaves doesn’t give much actual indigo powder. A few grams at the most.
The next day I added some soda ash and whisk/ agitate the solution to add air into it. Then add thiox to it. This step is the same as extracting blue dye from woad.
The end result of how deep the blue dye one gets depends on experience. the more you do it the more easier it becomes. The following year I grew more leaves from seeds harvested and in the height of summer I harvest a lot of leaves and ended up with some lovely blue dye.