Towards an indigo revival?

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Jenny Balfour Paul

Recently my guild was privileged to host Jenny Balfour Paul, a world expert on the history of indigo and its use by different peoples. That history is a global story of chemistry and dyes that goes back at least 6,500 years.

“It’s unbelievably ancient this dye. All the other dyes change. Indigo is always blue,” she said.

Balfour Paul’s lifelong study of indigo started mainly by chance as a project to document vanishing traditions so that when the time came they might be revived. Her work has taken her to Yemen, India, China, the Marquesas Islands and beyond.

“My life has been guided by a molecule. It’s a perfect molecule. Without indigo there would be no natural blue dye,” she said.

“Even indigo stories are based on chemistry. Indigo is invisible in the plant. It’s dyed cool not hot. It’s green in the leaves you have to extract the color with oxygen. No other dye does that. Everything about it is different. Indigo doesn’t absorb into fibers. It sits on top of it, in layers.”

But indigo’s story also has a dark side linked to slavery and exploitation, which in some areas is holding back its revival as an environmentally friendly alternative to chemical dyes. Balfour Paul does not shy away from this part of the indigo story, which she sees as the second part of the indigo tale.

The indigo miracle

Indigo vat

The first chapter in the indigo story is—broadly— the incredible story of how indigo pigment, invisible in its host plants, was detected, extracted and used by humans in the first place. Indigo shows up in different plants around the world. It’s the same molecule, but in Europe it’s found in Woad, in Japan it’s polygonum and in Mali it’s Lonchocarpus cyanescens.

How did humans happen upon this miracle molecule? No one really knows. What we do know is indigo dyeing traditions developed worldwide and many of them have since vanished. Or in the case of indigo dyeing in Yemen, it’s literally being bombed out of existence.

Slavery and exploitation
The middle of the indigo story is enmeshed with slavery and exploitation in the US, the Caribbean and India.

In the US, indigo was introduced into colonial South Carolina in 1740 where it was grown on plantations by slaves. It became the colony’s second-most important cash crop after rice.

Jamaica’s first colonial crop was indigo, again grown on plantations by slaves.

In India, farmers were forced to grow indigo and workers’ conditions were appalling. Indigo was big business and in 19th century half the exports from Kolkata were indigo.

That all came to an end in the early 20th century as synthetic indigo had almost completely replaced the natural pigment by about 1914.

Revival?

Shibori dyed with Indigo

Indigo has struggled to overcome its cultural baggage particularly in India, says Balfour Paul. She is optimistic however that the page has turned for indigo.

“Now it’s a story about revival and environmentally friendly dyeing,”she says.

In El Salvador indigo is now vacuum packed or canned as a paste. The revival of indigo in El Salvador being used by Gap, Levi’s and Benetton for baby clothes, because they know synthetic indigo is toxic, said Balfour Paul.

In 2013 Levi’s 511 collection featured organic, indigo-dyed jeans. People really need one pair of organic jeans, not 10 from discount retailers, says Balfour Paul.

Jamaicans are revisiting indigo and in Kolkata and throughout Bengal there are efforts afoot to reintroduce natural dyeing.

Sustainability and slow fashion are the way forward, said Balfour Paul: “I’m going with it.”

What’s next for Jenny?

Jenny Balfour Paul continues to follow the indigo molecule. She is now working now with Dominique Cardon—another natural dyeing superstar— on the Crutchley Archive at the Southwark Archive in London.

According to the University of Glasgow’s Centre for Textile Conservation and Technical Art History:

“Thanks to descendants of the Crutchley family who owned and ran a dye company on the south bank of the River Thames 300 years ago, rare records from this era have survived. The collection includes sumptuous pattern books with samples of wool ‘topped’ with red from madder and cochineal dyes, dyeing recipes and instructions, and customer names and amounts of credit.”

“In 1740 they could colour match as well as any modern dyer. The archive is full of dye recipes,”Balfour Paul said.

I personally can’t wait to see the fruits of their work. It’s bound to be fascinating for any student of natural dyeing.

Jenny Balfour Paul bibliography

Indigo in the Arab World (1996)
Indigo: Egyptian mummies to blue jeans (1998)
Deeper than indigo (2015)

Jenny on the Maiwa podcast

But how much mordant do you *really* need?

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This is THE question, isn’t it? I think a lot of people, myself included, just start with a formula they find somewhere but don’t take the time to test it against other options. The good news is, I’ve done a test for you. I’ve done a mordant strength test with aluminum acetate previously; this is a mordant strength test with potassium aluminum sulfate, aka, alum mordant for protein fibers.

My underlying question in doing this experiment is how best to handle wool, alpaca and silk blend roving— how much heat, agitation, time and mordant gives the best result? And do I need to use cream of tartar (potassium bitartrate)? My preferred outcome will be good color uptake while still having a nice hand and easy spinability.

The first recipe I came across was from John and Margaret Cannon in Dye Plants and dyeing, which uses 18% WOF alum and 6% WOF cream of tartar. I started using it and had good results, but in my natural dye class we use 10-15% alum with no cream of tartar. I usually bring my mordant bath up to temperature (about 160-170F), turn off the heat, and let my fiber sit overnight. In class (where we generally use fabric samples, not yarn or roving) the fiber is at constant temperature for an hour (170F or so— not boiling, but steam coming off the water) and then removed and rinsed. The least amount of alum mordant I’ve seen used is from Jenny Dean, just 8%, but with 6% cream of tartar.

This experiment is my fairly best comparison of apples to apples to apples, starting at the low end of 8% alum, ending at the high end of 18%, and splitting the difference at 13%. All mordant strengths are tested with and without cream of tartar, and processed at heat (170F) for one hour, or brought up to heat and then turned off and let sit overnight, for a total of 12 different samples. Both wool, silk, wool/silk blends and a silk/plant fiber blend were sampled, in the form of fabric and also commercially prepared organic undyed yarn. All samples of the same mordant bath were processed together, and all samples were wetted out for at least an hour. In the end, ALL of the samples went into the SAME dyepot of 20% WOF cochineal, a good strong dyepot, with the hopes of disambiguation.

There were some interesting results!

Even before I mordanted anything, the visual difference between the alum with/alum without cream of tartar bath was obvious. With cream of tarar, the bath was clear. Without, it had a cloudy, milky look. This persisted after the fiber was removed from the mordant bath. The ph of each bath remained the same, about 3-4.

After I’d mordanted my samples, but before I’d dyed anything, I tested  the hand, or feel, of all my samples— the common complaint about increased alum strength is that is can make the fibers feel “sticky”. With all of my wool samples, regardless of alum%, those without the cream of tartar felt coarser. The yarn especially felt sticky without cream of tartar. On the silk noil samples, the samples WITH cream of tartar at 8% mordant strength had a more noticeable yellow cast . The hand of the silk noil and habotai were not discernibly different, but the silk-faced plant blend and the wool/silk were definitely smoother/nicer with the 6% cream of tartar.

So what about the color? Take a look! These samples are all laid out in a 4×3 grid as follows:

8% 1hr, 8%/6% cream of tartar 1hr, 8% overnight, 8%/6% overnight

13% 1hr, 13%/6% 1hr, 13% overnight, 13%/6% overnight

18% 1hr, 18%/6% 1hr, 18% overnight, 18%/6% overnight

Silk/hemp blend— my “control”. In real life I’d use aluminum acetate to mordant this.

Silk habotai. The cream of tartar definitely helps the dye uptake, especially noticeable at the lowest strength mordant.

Silk noil. The unevenness of color I attribute to not enough wetting out time. In the future anything with silk will soak overnight.

This is a thin 60%silk/40% wool twill. I was surprised that I liked the 18%/6% 1hr mordant the best.

Medium weight wool challis. Not as great a difference between the 13% and 18% mordant strengths as on the silks.

Commercially prepared undyed organic merino yarn. I didn’t scour it, and I should have! I think the color uptake at all mordant strengths would have been much better. The 18% overnight skein is missing— I ran out of yarn.

Takeaways:

Its pretty clear that more mordant equals more dye uptake. This was a strong dyebath, with plenty of color left over (I dyed several more yards of fabric afterwards with the leftover bath). Between 13% and 18% the difference isn’t as stark as at 8%, so I might do an additional test at 15%WOF and see if I can see a big enough difference to merit the additional mordant.

It’s not so clear in the photos, but the samples mordanted on heat for one hour had a nicer, more even color than the ones brought up to temperature and then left to cool overnight. This surprised me. In the future I will probably keep on heat for one hour, then let cool naturally before removing the fiber. This has also dissuaded me from trying a recipe I found on the internet for mordanting in cold water!

I will definitely be wettting out silks overnight, and scour any fiber I haven’t already prepped myself. I will use cream of tartar, for both mordant uptake and nicer hand. The final test, of course, is a light-fast test. My hypothesis is that the higher mordant strength will be more fast.

Light-fast test in progress.

At this point I’m of the opinion that the prep work, from scouring through mordanting, is the key to nicely dyed fiber. The dye bath is basically proving how good a job I’ve done. A stronger dye bath won’t produce any more color than the amount of mordant bonded to the fiber. This test was done with cochineal, which won’t dye without some sort of mordant; if I was dyeing with something substantive like onion skin, the extra mordant strength may be unnecessary.

I hope this helps answer the question of how much mordant *you* really need: by all means, do your own experiments!

 

Surface Design with Natural Dyes

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Rachel: “I found these cute block-printed throw pillows I want to make. How can I do that with natural dyes?”

I’m mostly a spinner and knitter, but in the natural dye classes that I attend at OCAC, there are a lot of people who focus on textiles. We’ve used a simple technique to get a lot of different results, and it’s really a lot of fun.

You will need the items you wish to print with: print blocks, stencils, potato stamps, paintbrushes, silkscreens, or anything else, and a few pieces of equipment: a blender, a steamer, an old bedsheet, and gum tragacanth. Gum tragacanth is a natural product that is most often used making fondant for cakes. Here it’s used as a “sticking” medium. What’s good about gum trag vs. other similar products is that it doesn’t interfere with or change the color of your dyestuff.

The technique: mix up some gum trag and water in a blender. Say, 1/4 C gum trag and twice a much water. You will hear and feel the mixture get thicker after about thirty seconds. If it’s too thick, add more water. If it still seems a little runny, let it sit for a bit, it thickens over time. Don’t mix more than you’ll need for your project at hand, because it only lasts about a day in the refrigerator. (Obviously it will be easier to judge once you’ve done it, but a little medium goes a long way.) You will want it thick enough to adhere to your stamps, but not so thick that you lose definition. If you’re silkscreening, you’ll want the thickness of silkscreen ink. Make some practice stamps before you commit to your fabric!

Mordant Printing

You can mix a mordant into your gum trag mixture. We used very small amounts of copper and iron, and a slightly less small amount of alum during our classes.

Gum trag with mordants

Gum trag with mordants

Here is a thread spool print with copper mordant:

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Here I’ve printed on a silk scarf previously dipped in indigo with alum, using a feather for my print:2016-10-04-19-59-47

Here I’ve used an iron mordant on silk noil, again with feathers. I used an old paintbrush to apply the mordant mixture:

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Discharge Printing

You can mix and acid or a base into your medium to discharge color on an already dyed piece.

Gum trag with soda ash

Gum trag with soda ash

Here I tried using soda ash to shift the color on a pisolithus mushroom-dyed piece of silk:

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Here I’ve used tartaric acid to discharge the logwood dye on silk organza:

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You can do combinations of these techniques:

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Discharging with a print block

And printing with an iron mordant

And printing with an iron mordant

How to set your prints:

Lay out your dried fabric on an old cloth in a single layer, fold extra cloth over, and roll up, jelly roll style so that it will fit in your steamer basket. You want STEAM ONLY! Take care that the water is not getting into the bottom of the basket, and place a towel or piece of felt on top underneath the lid to keep condensed water from dripping back down. Make sure you’ve got steam going before placing your jelly roll in the steamer basket. Steam ten minutes, and remove carefully. Let cool until it’s comfortable to handle, then unroll.

Jelly roll in steamer basket

Jelly roll in steamer basket

Wash your steamed fabric in warm, soapy water to get the gum trag residue out. It still contains mordant, discharge or dye, and if the excess isn’t washed out it will go into your dye pot and change the result.

Here are some results after dyeing our prints. The yellow is from onion skins, the pink from Brazilwood, and the orange a combo of both.

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Here are my feathers. You can see that the gum trag wasn’t washed out completely by the extra dark muddiness around the onion skin feathers.

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I decided to after-mordant the whole piece in alum, and not only did that get rid of the excess print fuzz, it changed the color of everything. It’s a bit 1970’s decor now, but I think it will still make a nice pillow:

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For the discharge printing, you don’t necessarily have to steam the piece before washing. Here’s a sample of logwood on silk that I discharged by painting the back of a leaf with gum trag and citric acid, and then simply washing when I liked the result. It made a nice multi-colored effect:

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I steamed my Ph-shifted fabric, and once I washed it out it ended up being merely discharged. I think I would have had better results if I’d washed it out as with the leaf print:

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And here is a piece of silk crepe de chine that I silkscreened with alum and then dyed in Osage orange:

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So, to answer your question Rachel, you have a lot of options. You can make a mordant print on unmordanted fabric. You can make a (different) mordant print on mordanted fabric. I didn’t include any photos, but you can mix natural dye extracts with your gum trag and print directly that way, with color. You can discharge already-dyed fabric. And you can do combinations of these techniques. You’ll no doubt have noticed that all these examples are on silk, but many of my classmates used this same technique on cellulose fibers.

There is also the option of surface design using natural pigments, which I’ll cover in my next post.

Fresh Leaf Indigo

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The hardest part about dyeing with fresh leaf indigo is growing the indigo. One of the people in my natural dyeing study group did all the hard work, and brought it in to share. This is what fresh Japanese indigo looks like:

Japanese indigo, persicaria tinctoria

Japanese indigo, persicaria tinctoria

The leaves are picked off the stems:

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Then blended with ice water:

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And strained through a cloth (in this case, silk):

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We squeezed out the cloth to extract as much juice as possible, and this was our dye bath. We put our fiber in, a mix of wool, linen and silk:

Fresh indigo dye bath

Fresh indigo dye bath

We massaged the items in the bath occasionally, and let them sit in the bath about an hour. The bath began to oxide:

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We then removed the items from the bath and let them air out. The color slowly changed from green to blue on silks, a pale green on linen, and a dark blue-green on wool. The oxidation time was much slower than with a reduced-indigo vat.

This is the silk straining cloth:

Straining cloth after several batches

Straining cloth after several batches

Straining cloth after half an hour

Straining cloth after half an hour

Bonus round: we also used the leftover pulp from the straining cloth to  “paint” on fabric— basically rubbing it into the fiber like a grass stain.

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We let the pulp-prints dry and oxidize before rinsing. And although we did not do this step, here are instructions to precipitate out the indigo from a fresh bath, to use in a reduction vat. It’s a great teaching article using fresh woad.

Japanese indigo seeds are available from various places on line, and the plants like a warm, humid environment. Humid places can get several crops per season before the plants die. Places that are dry in the summer (like western Oregon) can get one crop during the growing season with irrigation.

Fun with Cochineal

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After indigo, I bought a cochineal dyeing kit which contained the bugs, several mordants and some vague instructions. (I say the instructions were vague, but really they gave several options as far as time vs. temperature in mordanting. It’s one of those things that once you know what’s going on makes perfect sense.)

Rachel and I did a test run when she was here last April (Sheep Cabana retreat: dye as much stuff as possible in 48 hours), and here is what we came up with:

Cooking and straining some cochineal bugs

Cooking and straining some cochineal bugs

We started with 4oz of dried cochineal (which is a lot), cooked them for about an hour and then strained the liquid into the dye pot. I saved the used bugs for later. Then we mordanted our wool. We used some white Shetland and some grey mohair locks, and mordanted with both alum and tin, by simmering our fiber in each mordant bath for about an hour. I would say that our mordanting pots weren’t large enough, because the tin-mordanted wool definitely felted.

The dye pot

The dye pot, onion bag of mohair locks on top

We could have used a bigger pot.

Viola!

Viola!

Here are the results, from top clockwise: tin mordanted wool, alum mordanted wool, alum mordanted mohair, iron after-mordanted wool, iron after-mordanted mohair.

Rachel left, and after a couple of months I got out the leftover cochineal bugs again and tried some more dyeing. (Those bugs sat on my patio in that plastic container, above, the whole time, ignored. I had no issues with them rotting or anything else unpleasant.) I re-simmered the bugs and left them sit overnight in the pot, and strained the bugs out in the morning. Then I did a series of successive dyeing on 50g each of alum and copper-mordanted wool:

Top, alum mordant Bottom, copper mordant

Top, alum mordant
Bottom, copper mordant

I heated the cochineal dye pot, added the mordanted wool and let it sit out on the patio here either all day or overnight. The total hands-on time was probably 1/2 hour.

Here it is spun up:

Successive alum mordant, left to right, with copper mordant wound into a cake far right. The orange is the immediately adjacent cochineal overdyed with weld.

Successive alum mordant, left to right, with copper mordant wound into a cake far right. The orange is the immediately adjacent cochineal overdyed with weld.

I’ve been taking some natural dyeing classes at the Oregon College of Art and Craft, and one of the neat things we did was dye with cochineal with no metal mordants. Instead we used 25% WOF of cochineal, 10% WOF powdered gallnuts (Gallic acid) and 10%WOF citric acid, all in the dye pot at once. Hot tip: we ground up the cochineal bugs and a little water with a mortar and pestle. No soaking required.

We simmered wool and silk noil for an hour and got these lovely colors. The cochineal strikes the wool and silk differently!

Shibori cochineal on wool

Shibori cochineal on wool

Left, wool, right, silk noil

Left, wool, right, silk noil

These are nice colors on their own, but I also wanted to experiment with this dyeing method as a base color. Here is the same fabric overdyed with indigo. One of the very interesting things about cochineal is that the color will shift from red to blue, depending on Ph. The middle samples are overdyed with indigo (about Ph 12) and rinsed, the far right are the same, but rinsed in a white vinegar solution (about Ph 3).

Cochineal overdyed with indigo

Cochineal overdyed with indigo

I also tried some after-mordanting, with iron, copper and alum mordants:

Left, iron after-mordant Middle, copper after-mordant Right, alum after-mordant

Left, iron after-mordant
Middle, copper after-mordant
Right, alum after-mordant

There is really a lot you can do with these little bugs, and a huge range of color, depending on what techniques you use. In other words, fun!

Autumn Leaves and Contact Dyeing

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Instructor’s sample of leaf contact dyeing

I had my first Natural Dyeing class at the Oregon College of Art and Craft last week. We started by walking the campus and collecting various autumn flora: fallen oak and maple leaves, pink-backed cherry leaves, fresh comfrey, spotted dying blackberry leaves, walnut hulls, tupelo, madrone and walnut leaves, Indian blood grass, and anything else that caught our eye. The ostensible purpose of this was to collect material to make our own contact dyed projects, but really it was to get us excited about natural dyeing. This time of year in the Pacific Northwest the ground is littered with dyestuffs, and the quick and easy method we learned yielded pattern as well as color.

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Once we collected our leaves, we laid them out onto fabric or paper, and either rolled up our fabric tightly around a stick (or for added color, around a rusty iron nail) or accordion folded and clamped for a shibori effect. These packets are then simmered in a water bath for an hour, and then removed and unwrapped.

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What I found most interesting about this technique is that there is really very little dye in individual leaves (for the most part tannic acids) but because of the wrapping or clamping, the color can’t migrate anywhere other than onto the fabric or paper. In other words, the opposite of leveling. In a lot of cases, the color transfer is more akin to printing— the fabric or paper is not really dyed per se, but stained or imprinted with the actual leaf color, giving pinks or greens which don’t exist as an actual dye. Our instructor cautioned us as much, saying that these colors will fade with washing or over time. That said, there definitely was dyeing of fabric around the periphery from the tannic acids, and also where the rusty nails provided an iron mordant.

Here is a leaf print where I had an iron plate clamped to the outside of my fabric packet:

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Leaf print on silk noil with iron plate

And likewise wrapped around a large rusty nail:

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Silk charmeuse leaf print wrapped around iron nail

Here is the difference of the dyestuffs on cellulose. For one, I didn’t get my packet wrapped tightly enough and the colors ran. For another, the yellows and greens remained printed while the tans of the tannic acids didn’t penetrate as much. I expect this to be a function of the density of the cellulose in paper form, and I would expect better tans on cotton yarn:

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Wrapped leaf print on paper

This technique also led me to revisit my forays into dyeing with candy. I’d encountered poor results with a lot of candies that contained very little dye. So I tried some candy contact dyeing:

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The candy melted pretty quickly, so it was hard to keep the fabric tight, but the dye migrated onto the fabric rather than into the dye pot. I can see some candy-related shibori in my future!

I’d also encountered  some inexpensive pomegranates at the grocery store last week, and per Rachel’s last post I bought them for some seasonal dyeing. Pomegranates contain ellegic acid, which are yellow tannins, so I thought this would be a quick way to see what sort of coloring I could get from them:

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This is one slice of pomegranate:

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Folded and clamped pomegranate slice on silk charmeuse

And here is multiple slices and layers, with the rest of the pomegranate in the dye pot:

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Folded and clamped pomegranate on silk noil, over some walnut hull spots

Tight wrapping and clamping is the key to good transfer, but whether you are preserving autumn leaves, testing dyestuff potential, or finding another use for seasonal candy, it’s such a quick and easy technique that it’s definitely worth trying.

On Mordanting

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Indigo is apparently the gateway drug of the natural dye world. It led me to try dyeing with cochineal, which should have led me to a better understanding of mordanting, except it didn’t. There are a lot of recipes, but not a fat lot of information out there on the science of natural dyeing. There is a lot of information on synthetic dyes. As it turns out, there is a good reason for this.

The history of synthetic dyes is also the history of organic chemistry, so the process of learning how to make synthetic dyes provided the chemical knowledge. The advent of synthetic dyes squeezed out the natural dyers’ guilds, so the new chemical knowledge wasn’t applied backward. There is a lot of good information out there on the invention of mauveine, the first analine dye. If you love history, how synthetic dyes changed the socio-economic world is fascinating, and it in part explains why there is precious little textile manufacturing still done in the US. Some of the more interesting monographs I’ve come across about the chemistry of natural dyeing are from India, Pakistan and Egypt, where there still are textile industries, and where scientists are taking another look at natural dyestuffs in order to have a more sustainable and less toxic impact on their environment. I’ve ended up learning about synthetic dyes, color chemistry, the quantum physics of color, synthetic fibers, and finally, mordanting and natural dyes.

That said, Maiwa and Turkey Red Journal are both excellent resources for natural dyeing information, including the chemistry, and they are both on the forefront of bringing the chemical knowledge back to the natural dye world.

So what is mordanting? If you are using metallic mordants, basically you are making your own acid dyes. Instead of using an acidic bath to promote ionic bonding as with synthetic acid dyes, the metal ions of the metal mordants have a similar polar effect. The mordants form covalent bonds with the color bearing compounds in the dyestuffs, which are the very strong bonds between atoms (sharing electrons in the outer shell). Since they are acid (polar) dyes, they therefore bond better with the positively charged amino acid chains (wool, silk) and poorly with cellulose (cotton, linen).

Tannic acid is a non-metal mordant, but “tannic acid” itself isn’t really a discreet chemical, but rather a broad heading under which several acids fall (which also happen to be tannins): Gallic acid, ellagic acid, and catechic acid. Most of the so-called “substantive” natural dyestuffs that require no mordanting have some form of tannic acid in them, for instance, sumac, pomegranate, fustic and cutch. Tannic acids bond well with protein fibers (think tanning hides), and also with cellulose plant materials. It also bonds well with the metal mordants, so plant fibers normally get pre-mordanted with tannic acid, and then again with the metal mordant.

I really wish I could tell you what chemical bonds are formed between tannic acids and these different fibers, but I’ve had no luck in finding scientific documentation thus far. I have to assume it’s not covalent bonding with cellulose just because fiber reactive synthetic dyes are so much more wash fast. I’m starting a natural dyeing class in October and I’m hoping to get to the bottom of this.

Nowadays aluminum acetate is available to mordant plant materials and the tannic acid step is debatable—this post and this post from Turkey Red Journal do comparisons of dyeing cotton cloth with different configurations of tannic acid/alum/aluminum acetate. Some of their considerations are cost and availability for dyers in poorer countries. Rachel does most of the cotton dyeing between the two of us, so I’m leaving it to her to take good notes on her findings.

 

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This monograph is great in detailing the chemical structure of wool. There is a lot going on in a strand of wool, aside from the positively charged dye sites. There are other chemical bonds that give rise to it’s strength and elasticity, and these are both things that can be affected by Ph, heat, and specific properties of different metal mordants like iron or tin.

There is a time vs. temperature factor in mordanting. A lot of recipes call for simmering your wool in your mordant for an hour, but that can easily lead to felting. Heating up your mordant and letting your wool steep overnight can often produce a more thorough saturation of the fiber and therefore more even dye uptake. Mordanting can take place before, during, or after the dyeing, but if it’s done prior to adding the fiber to the dye pot, there is more control over the mordant-to-fiber ratio, and the mordant bath can continue to be reused. This becomes more important when using the more toxic of the metal mordants, tin, copper and chrome.

Older mordanting recipes called for an excess of the metal mordants to ensure good dye uptake, in part because the strength of the mordant material was not guaranteed. Now we can source mordants with guaranteed strength and purity, so we can be a lot more precise and use recipes that leave little to no extra mordant in the bath. I did some trials with cochineal earlier this summer (that’s the next blog post). Using a recipe for a weighed amount of fiber, I tested my mordant bath to see if it was actually discharged (my copper did not seem to be), by adding more fiber to the “discharged” mordant bath and then soaking it in the dye bath and seeing if the dye strikes or not. When I was done I bottled up and saved my remaining mordant bath rather than tossing it out anywhere.

On hold for the next round of mordanting

On hold for the next round of mordanting

Once the mordant has bonded to the fiber it’s not going anywhere, so you can use different mordanted materials in the same dye pot, which is fun and interesting because you can see the effect the different mordants have.

Some metal mordants are toxic. Chromate poisoning is particularly unpleasant. Oxalic acid, often used to shift colors as an after-mordant is toxic. Synthetic “true black” acid dye is also toxic, as it contains chromium as it’s coloring component. None of theses things belong in the groundwater, or your septic tank, or near kids, pets or livestock. Entrapment is the state wherein metal particles are trapped in the steam from a water bath, and are then able to be inhaled, so don’t mordant in your kitchen. And for that matter…

Oak galls

Oak galls

A cautionary tale: we have a large tanoak tree growing next to the abandoned well out by our barn, and as a good source of natural tannins, I checked the interwebs for what the tannin concentration should be compared to oak galls, etc, for a possible recipe. What I found was that it wasn’t a tanoak. So I used a tree identification website rather than the book with illustrations I’d used initially, and the final question on the flowchart was “do the leaves smell like almonds when crushed?” Ironically as it turns out, this reminded me of the opening lines of Love in the Time of Cholera. My tree does smells like almonds when the leaves are crushed. It’s a cherry laurel, and when you boil the leaves you get hydrogen cyanide, which Nero used to poison his enemies’ wells. So. Back to collecting gall nuts.

The Science of Dyeing

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What is color? When I studied philosophy as an undergrad, it was always treated as a “secondary quality”, that is, something that’s not intrinsic to the nature of the thing itself. And while it’s true that how we see color is a subjective function of our eyes and processing in our brains, the colors of things is entirely dependent on the physical makeup of those things. When we see color, we are seeing into the atomic and subatomic nature of things. In other words, a tree is green in a forest even if no one’s around.

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To understand how color works, you need a little quantum physics. This monograph on color chemistry is concise, well-written, and with a little patience, accessible even for people like me who have only high school level chemistry and physics. If you are at all interested in how dyeing works, it explains everything.

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I’m also slogging through this one. It’s highly technical and I can only digest a few pages at a time, but it details all the general information in the first book. If you want more after reading The Chemical History of Color, then this is for you.

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To very generally sum up, the visible spectrum that our eyes can detect takes place in a really small range of wavelengths, from red to violet. Everything of shorter wavelength then the red range is the infrared, and everything longer than the violet is the ultraviolet. How these wavelength are generated or influenced happens at the quantum level, with the interactions of the electrons within an atom or a molecule. The electrons need to be understood as waves, not particles as I learned in high school chemistry. There are four or five different models that explain wavelength production, depending on the arrangement of electrons in their shells around the nucleus, and how they combine, or don’t combine with other atoms. What’s neat about all of this is that our eyes are seeing what’s going on at the quantum level! (That’s my take on it. I can’t think of any good reason why humans spend so much time and effort changing the color of things, if not to influence the building blocks of the world itself.)

Natural dyeing shows us that there are some plants and insects that impart good, lasting color, and some that are fugitive. The beginning attempts at synthesizing these color compounds were all trial and error, but now computer modeling can predict what wavelengths a particular molecular configuration should yield, and how to bind it to a particular fiber. It should be noted that two things dyers care about, light-fastness and wash-fastness are two separate issues. Light-fastness depends on the ultra-violet spectrums’s influence, whereas wash-fastness depends on the type of bond with the fiber (for the most part). Ultraviolet wavelengths can greatly influence the visible spectrum. We see this when colors fade in the sunlight. This often comes into play in natural dyeing (with black beans and berries for example)…one of the advantages of synthetic dyes is that they’ve been designed to be less susceptible to this effect. Another advantage of synthetic dyes is their leveling ability, that is, to dye evenly. They’ve been designed to bond weakly with the fiber so that they can actually un-bond and re-bond, rather than strike all at once in a concentrated area. Some of the molecules used to produce color are quite large, especially in the blue range. This is why even when using an acid dye, there is still blue left in the dye bath even though it is fully exhausted. The color producing part of the molecule is so large that it will actually break off from the part that bonds to the fiber during the leveling process. One of the mysteries of indigo is how it’s able to produce a blue color out of a relatively small molecule (there are several theories).

Synthetic dyes are often described as brighter than their natural counterparts. This is because the synthetic dye molecule is emitting a vary narrow, specific wavelength, where a natural dyestuff, as a complex plant material, is emitting a broader range of wavelengths within that color band. Different mordants also affect the color in natural dyeing. The metals used in mordanting not only have the necessary number of electrons in their outer shells to form covalent bonds with the dyestuffs, but of themselves have different wavelength properties…precisely because of how the electrons are composed around the nucleus of the atom. (This website/app of the periodic table is great. It shows everything you might want to know about each element, down to the electron spins in each orbit.)

Color aside, to understand how dyeing works, you need chemistry: the chemistry of the fiber being dyed, and the chemistry of the dye. Here are two excellent blogs that explain the chemistry of synthetic dyeing in simple terms:

Gnomespun Yarns

Paula Burch’s All About Hand Dyeing

Again to sum up, there are different types of bonds that can be formed, and they depend entirely on what you are dyeing: the amino acid chains of proteins, or hydroxide chains of cellulose plant material, maybe a mixture of both in the case of synthetic fibers, (or none of these in the case of polyesters). Animal fibers have positively charged receptor sites, so ionic bonding occurs with acid dyes (and also some hydrogen bonding, which is like ionic bonding but smaller). Plant material’s OH hydroxide chains don’t have the positve charge sites that animal fibers do, so fiber reactive dyes are designed to form covalent bonds, which are very strong, in a basic, rather than acidic bath. Disperse dyes dye plastics at high temperatures and pressures, although there are disperse dyes available for the home dyer that work in the dryer. Direct dyes work through a force called substantivity, and they need to be rather large molecules in order for this force to work. Since they are so large they are not particularly wash fast, and the colors are often duller. They are generally used on plant fibers, and are a component of all-purpose dyes like Rit.

This post by Gnomespun Yarns does a good job explaining the difference between animal fibers and plant fibers, and how it affects dyeing. This one by Paula Burch does a good job explaining the different types of chemical bonds that are made with the various types of synthetic dyes. They are both well written, with nice diagrams, and really explain why it’s important to know the chemistry of what you’re trying to accomplish.

All of this is by way of the next blog post, which is about mordanting. The chemistry of natural dyeing is only very recently becoming well documented, and I’ve found that understanding the technology that succeeds it is the most straightforward way of getting to it’s precursor.

 

Indigo-a-go-go: Better Dyeing through Chemistry

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I recently took a class on making an indigo fruit vat. The class was great, the vat is quick and easy and you can read how to do it here, but when it was over I was left wondering what’s going on in there?

The interwebs are sort of helpful, in that you can read all about what happens in the indigo dye process, but there appears to be an underlying assumption that dyers aren’t interested in the chemistry behind what they’re doing, so there’s not a lot out there that puts it in layperson’s terms. And they tell you chemically what happens, but not why it happens. Personally, if I know how a process works, I find it a lot easier to do the steps involved correctly, because it makes sense why all the steps are there. If I’m trying to get a bunch of molecules to do what I want them to do, it will be more efficacious if I’m not bumbling around blindly.

So I’ve spent a good amount of time looking for answers to this question, and what I ended up finding was that the ways and means of indigo extraction and dye methods mirror a lot of other human technologies— in the automotive world I call it the Technology of the Day.

This is indigo:

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This molecule is not what is found in indigo-bearing plants (and snails!). True indigo (indigofera tinctoria) and woad, for instance, each contain different indigo precursors— molecules that will turn into indigo once they’ve been oxidized.

This is indican:

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This is the precursor to indigo found in the indigofera tinctoria plants. The bow-tie shape is a glucose molecule.

This is indoxyl and this is what actually penetrates the fiber in the indigo vat. The bow-tie shaped glucose has been removed:

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When making an indigo vat from fresh plants, all that needs to be done is remove the glucose part of the indican, and you get the smaller indoxl molecule. This is what will penetrate the fiber, and then turn into indigo with the addition of oxygen. Putting the fresh plants in a vat and fermenting them will remove the glucose, because the yeasts from the fermentation will eat the sugar part of the molecule and leave the indoxl behind. Here is a not only a nice article about different indigo precursors, but also a step-by-step tutorial on how to dye with fresh woad.

The indigo can also be precipitated out at this point instead of attaching it to a fiber. This will be the powdered indigo. The main thing to keep in mind is that once it’s been oxidized, it’s all the same indigo molecule; even synthetic indigo is identical. (*Mostly. I’ll come back to this later.) There is a lot of socio-economic history surrounding the trade and use of indigo, and it’s really fascinating, and I recommend this book which lays it all out in great detail:

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The turning of soluble indigo-precursor plants into insoluble indigo is where we then go. The indigo can be moved around and traded rather than be tied to the place and season of the plant material. But it’s also one step forward, two steps back: that indigo molecule is not soluble in water. The indigo precursors in the plants are soluble, but in order to make indigo soluble, the oxygens on the indigo molecule need to form other bonds. The indigo needs to be turned into indoxl, then it can be worked into the fibers to be dyed. When the fiber in this dye bath is taken out and reintroduced into the air, lo and behold it oxidizes— it takes up the oxygen molecules from the air and turns back into the insoluble indigo molecule, where it is held fast by electrostatic bonds within the fiber. The best technical description that I found of how the indigo molecule bonds with fiber can be found here.

There are actually a lot of ways to go about making indigo soluble, and they all involve a reducing agent and an alkaline solution. This is the  indigo vat. There are a lot of reducing agents, some of them very effective, and also toxic. For instance, here’s the process for dyeing jeans. A reducing agent has free electrons that are readily available to bond with any oxygen in the vat, whether it be on the indigo molecule or oxygen from the air.

Indigo vats need to be alkaline. An alkaline solution simply has more OH ions than H ions:

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I couldn’t really find any good descriptions as to why the vat needs to be alkaline— what work are those OH ions doing? I ended up calling my brother in-law, who has a degree in chemistry: a reducing agent adds it’s electrons to form other compounds, so the oxygen bonds on the indigo are transferred and form alcohol chains with the reducing agent. Alcohols are very water soluble. The OH’s in the alkaline solution strip hydrogens off this alcohol group and we end up with the indoxyl. The OH ions are highly reactive, and essentially make the solution even more soluble. The more OH ions, the stronger the alkaline solution is (and the more careful one needs to be in using and disposing of it).

As there are a lot of reducing agents, so there are a lot of ways to go about this reduction, and you can see echoes of the original use of indigo-precursor plants: Fermenting urine is a tried and true method, because the ammonia in urine is already alkaline. Another traditional method is fermenting madder root and bran with soda ash or lye. Fermentations, aside from eating sugars in the original vats, also produce sulfur-containing organic compounds as by-products, which are effective reducing agents. As with any fermentation, you are relying on a process that involves time, often days, at a constant warm temperature. Not only do you have to wait to do your dyeing, but you must rely on a successful fermentation process. Commercial denim dyeing uses very efficient but also much harsher solutions, to the point where repeated dips in the vat need to be carefully timed so that the oxidized indigo already on the denim doesn’t get re-reduced and therefore removed again from the fiber.

I’ve made soap, and I’m not a big fan of dealing with lye, so I’d prefer a weaker base. I’ve successfully made an indigo vat with the madder root and bran, and washing soda which has a weaker Ph than lye. It took about 10 days to be ready to use, and it’s, shall we say, a little stinky. This is the Technology of the Day part: how to get the result you want as cheaply and easily as possible. Cheap and easy are relative terms— for instance, what’s the cost to the environment, or the person using a highly alkaline solution? When you are done with the vat, how are you going to dispose of it? As a home dyer, you can make these choices for yourself.

The fruit-vat method that I learned uses fructose from cooked-down fruit, which are reducing sugars, and pickling lime (calcium hydroxide) to make the solution alkaline. Fruit sugars are an expedient way to make a vat because they have free electrons available at the end of their chemical chains, and so are oxidized rapidly. Interestingly, sucrose, table sugar, will not work. Sucrose is a combination of glucose and fructose, but the way that chemical bond is formed takes up the free electrons at the ends of both chemical chains. Sucrose is not a reducing sugar. But water boiled down with fruits, dates, or honey and agave, all work well, and of course powdered fructose. Citrus doesn’t have a lot of fructose anyway, but the acids in citrus are also going to also going to make the vat less alkaline, so it’s not recommended.

So the sugars bonds with the oxygen, then the OH from the pickling lime reacts with the resulting molecules. Eventually the reducing agent gets used up: the sugar is turned into an acid and so is no longer a reducing agent. Addition of acid will change the Ph of the vat. The enemy of the indigo vat is air, because that re-introduces oxygen into the vat, which turns the indoxl back into indigo, and uses up the reducing sugars. Less introduction of air into the vat means a longer dyeing session. The vat needs to be kept warm, so that those molecules move around and react with each other, but not so warm that the reactions don’t take place. (The traditional fermentation vats would be at the right temperature anyway, to maintain the environment for the yeasts and bacterias.)

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*So it should all be the same color if it’s all the same indigo molecule. Yes. Except if the indigo is precipitated from a plant source, it’s not going to be 100% indigo. There will be other molecules from the plant and the surrounding soil in there as well. Depending on what they are can change the appearance of the color. Also, depending on what fiber is being used the color will appear differently, because of the way that indigo bonds with the space within the fiber. If it’s lustrous like silk or matte like cotton it will appear differently. Depending on how alkaline the solution is, the protein fibers of silk or wool can be damaged. Depending on how well the fiber is worked in the vat will also effect how the color appears, based on how thoroughly the indoxyl is actually worked in or not.

I’ve spent about a month since my indigo class trying to get answers to my question, and I finally feel pretty satisfied that I’ve learned what I wanted to know. This process has also shined a light on the fact that so many natural dye recipes are just that, recipes, without divulging the science and available technology behind them. My hope is to demystify the processes so I can dye with confidence and reasonable expectations. Cochineal, you’re next!