Growing and extracting Japanese Indigo Pigment

I grow organic Woad (Isatis tinctoria) and organic Japanese Indigo plants (Polygonum tinctoria) both of these are versions of cold climate indigo that grow well in Minnesota.  Neither are native to North America, but both grow well in the upper midwest.

Woad is notorious for spreading quickly. So quickly that it is considered invasive and noxious in many western states in the United States.  To learn more this is a detailed report of the plant, and you can find your state.  

While dyeing with fresh Indigo leaves is lovely, extracting and saving the pigment so that it is shelf stable is incredibly exciting to me. Below is the process I used this summer to process Japanese Indigo leaves into shelf stable pigment using the fermentation method.

In September, when the leaves of the Japanese Indigo are lush and plenty, I harvested almost all of the leaves.

This takes quite a while, so my friends helped!

The pigment in Indigo is in the leaves. At this point, you can remove the flowers and seeds and save them for the next year.

Freshly saved Japanese Indigo Seeds.

Then take a large bucket or tub, and place all leaves (remove all flowers and seeds) inside and add water to a few inches above the leaves.

Place a heavy stone or paver on top to submerge the leaves. Place the lid on top of the bucket, and let ferment for 3-5 days.

The liquid will look almost neon in color and smell very floral. This means it is ready for the next step.

Remove the plants now, and compost. Then you can move on to alkalize the liquid. Remove ALL plant mater from the bucket. This could take a while. Then, add about 1Tbsp slaked lime per gallon of water to this bucket. Stir to dissolve, then stir this liquid back into your large container.

Use caution when adding slaked lime to water, as the solution will be highly alkaline. Avoid splashing the liquid, and if it gets on your hands or skin rinse immediately with fresh water.

Now you can oxidize the liquid! Using a broom or rake to vigorously swish the water around. The foam will begin to turn blue - this is very exciting and means it is working! Keep agitating it for about 30 minutes. You will know to stop once the liquid turns reddish brown.

Then you can begin the process of straining the pigment out. I had ten large heat resistant gallon jars that I poured the liquid in, and waited a few hours for the pigment to gather at the bottom of the jars. I use a turkey baster and carefully remove the top layer of liquid, careful to not disturb the blue pigment that has gathered at the bottom of the jar. This will take multiple days. You can pour the final blue liquid into a baking dish and let it dry. Then I crack it up and pound it into a sediment - see below.

Indigo harvest! Now shelf stable pigment.

Woad harvest! Now shelf stable!