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Indigo First Harvest 2020: Step 3

August 26, 2020

If you're just joining in, make sure to start with the Step 1 post to get the outline of the process I'm using.

Step 3: Alkalyzing and Aerating

I put a straining cloth over my aeration tank (mosquito netting) to catch the majority of leftover debris.

I will strain it even more later.

For the quantity of indigo I process, I have several 100-gallon horse troughs from the local farm store.

Now it's time to add some hydrated (slaked) lime, and oxidize the indigo with a lot of agitation.

I take out a small bucket of the indigo water, add my lime, then throw it back in and begin to aerate the tank.

I typically eyeball the amount of lime to use. I will add some, aerate for a while, and add more until I get the indigo to flocculate.

If you want to measure, the general rule of thumb is about 1 Tbsp per gallon of water. You are aiming for a pH between 9 and 11.
A video of adding lime to the tank, and the start of aerating the indigo:

I like aerating by sloshing with a bucket, but sometimes I also use a paddle attachment on my cordless drill. Either way, the goal is to get the whole tank of indigo as oxidized as I can.

As the water turns blue, I check in from time to time to see if the indigo is turning blue and beginning to sink.

	This is what the water looks like before adding lime...
	And this is what it looks like after lime and aeration. If it's still a little green, add a little more lime and keep agitating!
	When you let it sit for 5 minutes or so, you will see that the indigo sinks to the bottom.
	Before and after
	Very blue! I now have the indigo pigment we will save for dyeing later.
	It's hard to tell from this image, but once enough lime is added and you've aerated long enough, you can see the swirls of indigo. The trick is, the more lime you add to the indigo, the more lime you will have in your final product. If you're trying to produce a darker, more pure indigo, then make sure to add lime more slowly, check the pH more carefully and give it plenty of time to settle before deciding to add more lime.