Mood Indigo, the Old Sig Vat
Experiments in Blue-Dyeing the
18th Century Way

When I became a living-historian in 1974, my first concern in creating my 18th century wardrobe was to get the cut of my clothing period-correct. I soon began to make all my clothing in the proper natural fibers. In 1979, when I took on the responsibility of advising the volunteers at the Colonial Pennsylvania Plantation on the accuracy of their period clothing, I found myself being asked questions I couldn't answer on which colors were appropriate and which weren't. Thus began my interest in natural dyeing, specifically in researching and replicating 18th century dye substances and recipes. I've been naturally-dyeing clothing yardage and needlework threads for my 18th century projects ever since!

Indigo was one of the most commonly used dyestuffs in 18th century America, so although it has a reputation for being a challenge, I knew I had to try it, and the period way, using stale urine, aka "chamber-lye" or "sig".

What makes indigo dyeing a challenge is that it involves some tricky kitchen-chemistry.. The active ingredient extracted from the dye-bearing plants is indigotin, which is insoluble in water. However, when reduced in an alkaline solution, it loses an oxygen molecule and becomes "indigo white", which is soluble in the alkaline bath. Fibers immersed in the bath absorb the soluble "indigo white" Then, when they are exposed to the air, the molecule re-oxidizes, turns blue again (it's like magic!) and the indigotin, now insoluble again, remains fixed in the fiber.

There are many modern recipes for indigo vats, but the traditional indigo vat is a fermentation process. In its most basic form, all you need is natural indigo, stale urine, and a good cozy spot with a comfortably warm temperature for the fermentation.. The urine provides both the nutrients to nurture the bacteria which reduce the indigo, and also the ammonia which creates the alkaline solution.

My first indigo-urine vat was based on a recipe in Nature's Colors, Dyes from Plants by Ida Grae. It called for stale urine "boy-child, collected in the morning". My son was a toddler in the summer of 1980, and still in toilet training, so it was easy to collect his first-morning urine and save it for the purpose. Once, I asked his pediatrician why "boy-child, collected in the morning" urine might be preferred. He said that that children have a higher metabolic rate than adults, so their urine would be more concentrated, and that early morning urine is the most concentrated of all. But boys'? That, he laughed, was simply easiest to collect! I dyed hand spun wool yarn for stockings in that vat, and quantities of Paternayan needlepoint yarn in several shades of blue, from pale to deep, the last of which I just used up in a flamestitched Bible cover.

Well, 23 years later, I finally had a chance to do it again. I put together a urine-indigo vat in the summer of 2003, incubating it in the trunk of my car, and I now have some gorgeous deep blue silk threads for Queen-stitching a new pinball, new skeins of needlepoint yarn in assorted shades of blue, several silk neck-handkerchiefs, all in different shades of blue, and a pair of blue cotton stockings.

After dyeing these, I thought I'd gotten my money's worth, so I decided I'd exhaust the pot by throwing in a pound or so of my hand-spun yarn, which had been dyed yellow with alum and goldenrod. That yarn came out an even, rich, deep forest green, so I got some more silk scarf blanks, since the pot was still goin' strong even into September, when it was no longer re-fermenting but still yielding good color. It was so much fun and so satisfying!

As I said, there are several different ways to reduce the indigotin molecule to its soluble state.Gina Gerhard did an indigo pot using lye and hydrosulfite at the Daniel Webster Birthplace Dyeing Workshop in 2001, out of which I got a nice tie-dyed bandannoe and "The Tie-Dyein' Indigo Blues". Of all the methods, the urine fermentation vat does seem to be the oldest, or at least the oldest still in use. Although I'd done the indigo-urine vat successfully before, I still found Jim Liles' book The Art and Craft of Natural Dyeing, Traditional Recipes for Modern Use to be extremely helpful in explaining why the sig-vat works the way it does and how to help it along.

A urine-indigo vat is actually quite easy, despite its reputation. It doesn't require bravery or wizardry, just intestinal fortitude! In New Hampshire I have to hurry to get it going in the early summer and finish it up before the cold weather sets in--my family won't permit it inside the house because of the smell.

Here is what I did:
I saved up my early-morning urine for about six weeks, The more concentrated the urine you start with, the better. If you can get children's early-morning urine so much the better, but mine worked fine. I collected it in a cheap plastic pint-measuring cup from the dollar-store, then transferred every morning's collection into a gallon jug. Each time the jug was full, I took it outside and emptied it into a clean white plastic five-gallon bucket with a good, airtight, snap-on lid. Once I had about three gallons of urine, I sewed 2 oz powdered natural indigo (Liles says some synthetic indigos won't work) into a small fine linen bag, sewed it shut and suspended it by a heavy thread from the bucket handle, so I could find it easily. A pair of rubber gloves was designated "indigo-only". As per directions, I rubbed the submerged indigo bag between my rubber-gloved fingers twice a day till the powder dissolved. I got my indigo from Dharma Trading Co. and I must say it was excellent quality, dissolving entirely with no residue. Once the indigo dissolved, I let the bucket sit three or four days in a warm place till the vat had a floating iridescent blue scum, and it was ready to use. You'll know your indigo vat is ready when you see that scum, and when the liquid is a greenish-yellow. If the liquid is blue, that's the sign of unreduced indigo.

When using the vat, it's best to introduce as little air as possible-no bubbles, no stirring, no sloshing-so that your reduced indigo-white doesn't become oxidized prematurely. I presoak my fiber or textile in a little stale urine, squeeze it out (using the gloves!), then, holding it squeezed, gradually lower it into my vat and open it out under the surface of the liquid. I use a stick to coax down any parts which want to float. There's always some sediment in the bottom of the vat, so I gently work the fiber around in the liquid to even out the tendency to spottiness. The amount of time the fiber spends in the vat can vary from ten minutes to overnight. Then, using the gloves, I grab the fiber under the liquid, squeeze out any excess liquid, and still squeezing, lift it up into the air. A bright, breezy day is optimal for reoxidizing the indigotin.

Click images for larger view.

Presto, the fiber goes from yellow to green to blue!

Twenty to forty minutes is a good amount of time to let the fiber air out. Deeper shades can be achieved by repeating the process. Two overnight "dips" was sufficient to give me rich, lovely blues; four overnight "dips" yielded a really dark navy-blue..

Over the course of the summer when the vat got sluggish I suspended some madder twigs on a string--Liles explains that madder-root naturally contains bacteria which activate the indigo fermentation. Once I also fed it six chopped dates, which is a technique I had learned from Ida Grae's book. (Liles suggests a teaspoon of Karo syrup instead of the dates, and a little dry cake yeast as an alternative to the madder root, but I've never tried these.) Since I was hydrating everything I dyed with a pre-soak in stale urine before putting it in the vat, the vat got a replenishment of a little 'new' stale urine from time to time. I dyed about two pounds of fiber and was still getting good strong colors--the dyeing season ended with the onset of cold weather and the vat nowhere near exhausted. The essential part is to keep the vat warm enough to ferment, about 90-95o F. To accomplish that in New Hampshire I had it in a closed-up garage for awhile, and ended up keeping it in the trunk of an unused car. ["Oh, honey? Can I use your car this week? Mine's incubating an indigo pot!"]

What I like about the fermentation vat is that it's gentle on the fiber and requires little effort--I can put in a pound of yarn or a silk scarf, work it about, then come back 24 hours later, air it for 20 minutes, then do it again if I wish, and voila! Nice rich blues! If you use yarn pre-dyed with fustic, weld, osage orange or goldenrod, you'll get some deep forest greens. You can pre-dye cochineal pinks to get lovely purples. Liles recommends 'finishing' protein fibers with a weak vinegar rinse to neutralize the alkali. I had never done this before, but who am I to argue with Jim Liles? So I did, and it does seem to set the color better. It's all so easy!

Admittedly, my plastic bucket, rubber gloves and automotive-incubator are not exactly period-correct tools, but the process is. All you'd need to do is substitute a lidded barrel and a hearth-side warm spot, and you'd have a properly replicated eighteenth century home-dyeing "blue-pot" set-up suitable to a historic site or reenactment.

My husband got to admiring the colors, and decided he wanted a necktie. And I used that pound of deep green handspun yarn to knit myself a contemporary vest. The nice thing about natural dyeing modern clothes is that any unevenness of color adds charm, and is not considered a flaw!

The usual caveats apply as with any other indigo pot--don't introduce any more air than you can help, work the fibers under the liquid to prevent spottiness, watch your vat for the signs of too much oxidized blue indigotin in the liquid, and so on. Also, you must keep this vat at a warm enough temperature [~90-95o] as much as possible for efficient ongoing fermentation. It's important to remember that using a sig-vat is like making wine or yeast-risen bread-you're working with the cooperation of micro-organisms, and you want them to be comfortable and happy!

I found many good suggestions in Lile's book, like pre-wetting the fibers in urine, and the vinegar-solution after-bath. His 'troubleshooting' section is excellent. But be forewarned, the vat will smell much worse than you imagine. My sig vat was still going strong in the autumn, despite ambient highs in the low 70's and lows in the 40's, so even though it was no longer refermenting, I was still using it with good results when real freezing weather obliged me to set it aside for the winter. The family simply wouldn't consider my bringing it into the house, not even in the cellar.

When I opened up the bucket in April 2004, the liquid was clear, with a thick blue sediment, and no smell. It looks as though I have to start again, from the beginning. Not a problem! A new bag of indigo powder from Dharma is a small expense, and urine is free! So beginning another sig-vat for Summer 2004 is no big deal, just an excuse for more adventures, and more of the joy of watching indescribably beautiful blue hues appear on my fabrics like magic!

Further fun in the blue vat, I dye some stocking-weight yarn for "self-striped" stockings.


1. The yarn, half in and half out of the sig vat.   2. A skein of self-striping yarn, airing in the breeze.

Suggested Reading: Books for When you've got the Blues

Balfour-Paul, Jenny, Indigo, Fitzroy Dearborn Publishers, Chicago, 1998

Grae, Ida, Nature's Colors, Dyes from Plants, Macmillan Publishing Co. NY 1974

Liles, J.N. The Art and Craft of Natural Dyeing, Traditional Recipes for Modern Use, The University of Tennessee Press, Knoxville 1990

Sandberg, Gosta Indigo Textiles, Technique and History, Lark Books, Asheville NC, 1989


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