Making a Ferrous Vat with Fresh Indigo Leaves

Q: I grew some indigo plants and i’d like to make a ferrous vat so I can do some dyeing. Can you tell me how?

A: I have a resource page with lots of information on different ways to dye using indigo plants here: https://www.grahamkeegan.com/i-grew-some-indigo-now-what.

A quick sketch for making a ferrous vat with fresh indigo plants is as follows: soak your leaves in a 5 gallon bucket for a couple days until the leaves lose their color, then remove the old leaves and stems and keep the liquid. Add about a tablespoon of slaked lime to the liquid in the bucket, then aerate it until it turns dark blue. Once you've got the indigotin formed (dark blue liquid) then you can decant a gallon of the liquid, heat it to simmering, add 100g Ferrous Sulfate and 150g Slaked Lime, cover and let cool for a half hour before adding back into the larger bucket. Then let the bucket rest (though stirring intermittently) for an hour or so before trying to dye in it!

If you are unable to heat your liquid during this process, you can add the lime and reducing agents at room temperature, but without heat the chemical transformation can take as long as24 hours to complete whereas with heat it only takes an hour.

Keep a lid on the vat at all times and keep the water level up as high to the lid as you can. If you need to top it up, use boiling water.

Clarification on Indigo Extraction

Q: I have a question about getting indigo pigment from the indigo I grew. I saw the PDF you have on your website where you alkalize and oxidize. At the end it says to prepare your vat or let dry. How do you dry? Do you leave it in the container with the lid open? I also was wondering if the size of container mattered? Is it better to do in small batches instead of a large amount? Also, how long is the shelf-life of the extracted pigment if I am not yet ready to make my vat?

A: If you let your pigment settle for a few days you can pour off the liquid on top. You can then put the remaining concentrate in a container and further boil it off or just let it sit out to dry. There’s an indefinite shelf-life so no rush to make your vat. Just keep the dried sediment in a jar in a cool place and out of the sun.

I would suggest doing bigger batches if you can. Small batches yield verrrrry little pigment each so the bigger the batch, the fewer times you’ll have to do the process!

There are some posts on my Instagram (@yesgraham) with shots of the indigo extraction process. You can also find information from other folks on Instagram using these tags as well: #indigoextraction2017, #indigoextraction2018, and #indigoextraction2019.