I’d like to share with you my experiments with extracting indigo pigment from fresh leaves. I dried most of my leaves so I didn’t have a lot to work with. My results are not conclusive, I still need to work on my method to get it down, but it is an interesting process.
I would like to use my homegrown indigo without a chemical reducing agent (hydrosulfite). Processing Japanese indigo by the traditional composting method requires a lot of volume and will not work for someone with a small crop. Instead I am extracting indigo pigment from my plants. The pigment can then be used in any indigo recipe.
The first step is to soak the fresh leaves in warm water. I tried this in various ways, for a couple hours, overnight, and for a couple days. I think next time I will try letting them ferment for a while. They released a brownish yellow color into the water with a little sheen on top.
Next, I strained out the liquid by dumping the leaves into a bucket lined with a nylon mesh bag from a paint supply store. These bags work great, BTW! I squeezed as much juice as I could from the bag. When you squeeze the leaves a gray blue liquid comes out. There is still a lot of indigo in these leaves so I returned them to soak and extract a second time.
The next step is to aerate the indigo juice. I started by pouring the liquid back and forth between two buckets 20 times. I added calx water (mix the lime with water, let stand, use the clear liquid) and added enough to get the ph up to 9. For some of my attempts it was a little higher, more like ph 10. When the calx water mixes with the indigo liquid, it turns greenish.
Just pouring it between the buckets to oxidize has not worked for me. I have to whip more air into the indigo juice. I have tried using a blender and a stick blender, but have settled on using an electric mixer and beating it for 15 minutes. Whew!
I am always hoping the mixture will turn blue, as it did in Michel Garcia‘s workshop using dried indigofera leaves. But instead it is mostly olive greenish with a little blue around the edges. When I am done mixing, I put it in large glass jars out of the light to settle out for a couple days or more, up to a couple weeks.
When the pigment has settled, I pour it into a colander lined with a cotton cloth. I have not found it necessary to decant the mixture, as Jenny Dean suggests. When the indigo particles are really ready they will sit on the cloth and yellow liquid will drain into the bucket. If the liquid that drains out is greenish, there is indigo that still has not separated…I would put it back into the jar to settle some more. The idea is to separate the pigment, which is blue, from the yellow liquid.
Here is where I am having difficulty. Sometimes the pigment that separates is blue, but frequently it is green. I have tried putting it back into a jar to settle more, sometimes that helps, sometimes not. Do I need to beat it longer? Add more alkali? Soak the leaves longer? If anyone has any suggestions I’d like to hear them. I plan to keep working on this with next year’s crop of leaves to get more consistent results. I believe that even if the pigment is greenish, it will still reduce in an indigo vat.
After the pigment is collected in the cloth, it can be used as a paste, or dried and ground to a powder. Then it can be used in any indigo recipe. I have been working with the organic indigo recipes developed by Michel Garcia. It’s amazing that something as ancient as this blue dye still has mysteries left for us to discover.
Be inspired by the mystery!