Indigo magic: a fruit vat challenge featuring persimmons and citrus

This year I gave myself the ultimate indigo challenge: create and maintain an indigo vat with plant-based indigo and fruit reducers from my family’s persimmon and citrus tree fruit discards, in an attempt to have a healthier ecological process. Basically, aside from growing my own indigo plants, the slowest and most labor-intensive type of indigo vat. But maybe also the most rewarding? In this post, I share lots of photos and a video of my experiments with building and maintaining a fruit-based indigo vat. 

Jump to: 

• Vat building basics 
• Building a fruit-based indigo vat featuring persimmons
• Checking and testing an indigo vat
• Dyeing with a fruit indigo vat: watch a video of the whole process! 
• Maintaining a fruit indigo vat with fruit/plant reducers 

Vat building basics

Indigo vats have 3 basic ingredients added to water: indigo, a reducer, and a base. Learn more about indigo chemistry here.

Indigo	Reducer	Base
Options: 1) Plant-based indigo powder (like this or this) 2) Plant-based indigo cake 3) Synthetic indigo powder (like this and in this kit) Note: indigo hair dye is mostly dried powdered leaves and not extracted, purified pigment sold as textile/fiber dye.	Options: –Fruit with high in fructose and/or pectin, such as pears, figs, grapes, bananas, dates, citrus peels. –Vegetables, such as sweet potatoes, carrots, turnips, zucchini, beets, sweet onions. –Other plants high in sugars and pectin, such as henna, madder root and rhubarb root. –Fructose powder: purified sugar. –Minerals: iron or zinc. –Microbes + fermented plants such as Alkalibacterium species in wheat/rice bran or sukumo indigo leaves. –Synthetic reducers: sodium hydrosulfite, thiourea dioxide.	Options:  1) Calcium hydroxide or calx (pickling lime) 2) Soda ash (slower but less eco-impact) 3) Lye (very caustic; handle with care)

The process that all these indigo vats follow include: 

1. Fill the container (or “vat”) with hot tap water slowly to avoid adding air.  
2. Add the prepared reducer and stir in. 
3. Add the indigo. If it’s a fine powder, sprinkle it on top and stir in to mix well.
4. Add the base. Sprinkle it on top and stir in gently to avoid adding air. Check the pH. 

Indigo reduces best in warm water (~120-140° F) and at a pH around 12. 

Here’s what my mini fruit vat looks like in cross-section. I used plant-based indigo powder, citrus peels as the reducer, calx as the base, and a glass quart jar as the container: 

For more detailed instructions on how to build various vats and get ingredients, check out Maiwa’s excellent and free “How to Dye with Indigo” guide (PDF here). I’ve been learning and honing my foundational indigo dyeing skills with their classes and instructors. 

Building a fruit-based indigo vat featuring persimmons

I followed these steps to create a fruit reducer out of overripe and fallen persimmons, then strained it into a 5 gallon bucket to start the vat. I then added hot tap water, finely ground indigo, and calx to raise the pH to 12.

1. Gather 3 kg (~6.5 lbs) of overripe and fallen fruit. 

2. Cut out moldy and buggy parts, take out peels and pits and save the fruit pulp. The peels and pits contain tannins that will change the color and chemistry of the indigo vat. 

3. Mash the fruit pulp into a pot. You can also blend into a smoothie if you’d like (I didn’t do this).

4. Cover the fruit pulp in a pot with a generous amount of water and boil for 30 minutes. 

5. Strain the boiled fruit mash into a 5 gallon plastic bucket. Save the strained fruit pulp for a second extraction.

6. Add hot tap water to the vat until it’s 3/4 full.

7. Add 80 g of indigo. If it’s finely ground (as mine was), just sprinkle it on the surface of the vat and stir it in using a vortex motion to avoid adding oxygen. I added it in 2 batches so it wasn’t too much to stir in at once. If it’s a coarser grind, then first hydrate it in a sealable jar with warm water and marbles and shake. Then strain it into the vat. 

8. Add 80 g of calx by sprinkling it on the surface and then stirring in gently with a vortex motion.

9. Heat the vat to 120° F (50°C) with an immersion heater (avoid going above 150°F (65°C). Stir gently several times, and then leave it overnight to reduce. Meanwhile, boil the saved fruit to make a second extraction and save the strained liquid in jars. Store the jars in the fridge and/or freezer to add to the vat later. It will keep in the fridge for 1-2 weeks and in the freezer for months.

10. By the next morning, the vat should have a metallic sheen on the surface and the liquid should be a clear yellow/amber. It may or may not also have a dark blue indigo flower. These are all signs that the indigo is reducing.

The fruit vats are slower reducing, so it’s best to wait 1-2 days before using. I use cotton knit test strips dipped one time for 10 minutes to check how the vat is dying. My first test strip one hour after I made the vat was a light blue, while the test strip on Day 2 was a medium-dark blue, and the test strip on Day 6 was a very dark blue: 

Checking and testing an indigo vat

Quick vat checks 

I do quick vat checks whenever I’m in my dye space, usually a few times a week, just to make sure the vats still have what they need to stay reduced and in decent shape to dye. I do a vat check and a test strip before I plan to do a dye session. 

Before stirring, I:

1. Check the surface for signs of an appropriate pH and adequate indigo reduction:
   1. A bronzy metallic surface layer that stays separated when you draw a spoon or finger through it.
   2. The indigo “flower,” which is a dark blue patch of oxidized indigo bubbles. An indigo flower comes and goes and its absence is not necessarily a sign that your vat won’t dye. The flower’s presence is helpful to determine if there’s enough reduction and/or indigo, but its absence is not. A test strip will help you assess this. 
2. Check the temperature. If <80°C and not reduced enough, sometimes heat will help reduction.
3. Check pH, with the goal to be 11-12 for optimal reduction and cellulose dyeing (such as cottons). If the pH is <11 and I plan on dyeing cellulose fibers, I’ll add a tablespoon of calx and recheck. I have found that my fruit vats reduce and dye much better at a pH of 12, so I aim for pH=12.
4. Check the liquid with a white or stainless steel spoon: it should be a clear yellow-amber color that oxidizes to a green-blue when taken out and swirled around to introduce air. If the liquid is a murky green or blue, I will check a test strip because this usually means it’s not reduced enough and needs more calx, heat, or reducer (which I will add in that order). 

Before a dye session, I check a test strip with one 10-minute dip. I usually stir the vat at this point to get the ingredients to mix with each other and distribute the strip more evenly. 

1. To make the test strips, I cut up a scrap piece of cotton into lots of 3” strips and have them readily available so I can compare the same fabric against previous test strips. I wet out the test strips in a small container of water and squeezing excess water out before dipping into the vat for 10 minutes. I stir the vat when I first put the test strip in and mid-way through at 5 minutes. 
2. After 10 minutes, I gently fish out the test strip with my stirring spoon and gloves and squeeze out excess dye. 
3. I do a very quick rinse in cold water to remove fruit reducer and indigo debris. 
4. I set the test strip on the counter to fully oxidize and label each strip. On the label I usually include the date and time, vat, temperature, pH, dip time (e.g. “10 mins x 1”), and fabric type. Since wet fabrics are darker than dry ones, I either wait till the test strip is dry to compare or wet the previous one to compare more accurately. 

The video below shows me checking the vat and dipping and oxidizing a test strip.

Dyeing with a fruit indigo vat

My shibori (fabric folding) skills have improved since I first learned a few techniques several years ago (here’s my first shibori post from 2022). One of my tip top favorite shibori designs is still the kikko itajime technique, in which we fold and press the fabric into equilateral triangles to create a “turtle shell” pattern. 

Here are the steps shown in the video to dye a kikko shibori cotton bandana in the fruit vat: 

1.  I fold a 24”x24” cotton bandana into equilateral triangles and bind it with chopsticks and rubber bands, my new favorite kikko pattern. This creates a lovely series of hexagons, which I think looks even more like a turtle shell. 

2. I then wet out the folded and bound piece in water, squeeze out the excess water, and gently dip it into the fruit indigo vat. 

3. I “massage” the dye into all the folds and crevices of the piece so all the exposed parts can get some indigo dye. This is a technique I learned at the Zhuo Ye Cottage (卓也小屋) in Nanzhuang, Taiwan, near where my family is from. After I finish massaging for about 2 minutes, I let the piece float in the vat for 3-5 minutes, then repeat the massaging. It’s time consuming, and you don’t have to massage, but I find that my pieces look so much darker and bolder when I do. 

4. After 10-15 minutes in the vat and 2 rounds of massaging, I gently take out the piece, squeezing the piece near the surface of the vat to avoid splashing and introducing oxygen. I then allow the piece to oxidize on the counter for at least 30 minutes, and sometimes overnight. If there’s a lot of debris on the piece, I’ll do a quick rinse in cold water, which speeds up the oxidation process too. 

5. I repeat the dip steps 3 and 4 above two more times. I find that on a medium to strong indigo vat, I can get dark, color-fast blues with 3 dips that are 10-15 minutes each.  

6. After the final dip and oxidation, I take off the rubber band and chopsticks for the big reveal! This is the best part. No matter how many times I’ve done this, it is always super fun. 

Maintaining a fruit indigo vat with fruit/plant reducers

To keep my fruit vat going with indigo reduction, I make more persimmon juice by boiling the persimmon pulp I froze in water for an hour, then straining out the chunky bits and adding the juice and small fruit bits to the vat. I reduce the amount of oxygen I introduce to the vat by pouring the juice slowly against the vat wall to avoid splashing. 

When I ran out of my family’s persimmons this spring, I started researching other local fruit I could use as reducers. I wanted to prioritize fruit discards that would otherwise be wasted or composted. I didn’t want to buy or use fresh fruit that we can eat or use tropical fruit that doesn’t grow locally (like bananas). 

Happily, after researching the fructose content of various fruit and digging into other people’s experiments, I found out that orange and grapefruit peels work well as reducers due to their pectin content, so the thicker the pith, the more the pectin and the better the reduction. Luckily, my family grows a variety of oranges, grapefruit and pomelos with thick rinds and lots of pith, so I was able to make citrus peel reducer for my persimmon vat and have enough left over to create a dedicated 3-gallon citrus peel vat that I can more easily carry around for teaching indigo dyeing workshops. 

Sometimes, I’ve added small amounts of fructose (about 2 teaspoons or 12 grams) to get darker blues for a dye session when my fruit reducers are going slow and/or I’m running low. However, I will try to not get lazy and throw in a bunch of fructose instead of making whole fruit reducers. It’s like feeding my fruit vats ultra-processed fast food instead of a healthy diet of real fruit. As my Maiwa indigo teacher says, “The fructose recipe is not great for longevity – almost like it has a sugar crash – whereas a slower reducing agent of the real fruit vats means you can keep it going for much longer.” 

Now that I’ve discovered that citrus peels, including dried citrus peels, make an effective indigo reducer, I asked my family to save and dry their citrus peels for me. Luckily, they are game for this funny request, and now my indigo vats have a steady supply of real fruit reducers. Yum!