Natural Indigo Blue Dye Origin Dying Procedures Technology and Dye Recipes for Denim Fabrics

Production with reproducible parameters with natural indigo dyes

Karl Mayer took over the patents for the innovative indigo dyeing technology from Master in 2018. There followed extensive works for further development and fine-tuning. One of the milestones in this context was the putting into operation of a pilot machine at the Denim Competence Center in Mezzolombardo, Italy, at the beginning of this year. The dyeing system maps the industrial production process at a scale of 1:10 and it has already supplied the first warp beams. These beams were processed by an Italian partner from the weaving industry, the result being highly promising jeans samples.

Enzo Paoli, Managing Director of Karl Mayer Rotal, wants to now use these fabrics in order to gain the interest of denim manufacturers in the innovative Green dye technology: “Only with samples produced under realistic fix running parameters can convince the market.

Why is Indigo different? It is not water-soluble. It is a substantive dye, needing no mordant, yet the colour achieved is extremely fast to washing and to light. Indigo is one of the most ancient and revered of all dyestuffs. The three recipes here all tell you how to dissolve Indigo, and how to dye with it. Deeper history and chemistry may be found in any good dye book.

Recipe #1 and Recipe #2 are quick, reliable, and very colourfast. Recipe #3, the fermentation method, is slower and less certain—but it’s the easiest method to start with.

Recipe #1: INDIGO HYDROSULFITE VAT

First a note about the chemicals. They should be treated with care and common sense but without panic. Keep them dry, out of children’s reach, away from food and use clean dry utensils for measuring. Always measure the water first, into a clean container; then add the chemicals to the water, so that you start with a weak solution and gradually get stronger.

MATERIALS:

• 2-quart glass or enamel pan
• candy thermometer
• enamel dyepot
• stirring rod
• 2 glass jars — 1-quart size

CHEMICALS:

• Sodium Hydrosulfite (or Thio-Urea Dioxide)
• Sodium Hydroxide (also known as LYE)
• Natural Indigo, powder or cake or paste (Cake Indigo must be pulverized before you can dye with it.)

CAUTIONS:

Lye is very caustic. Wear rubber gloves, don’t splash, especially keep out of eyes.

Solution One: Sodium Hydroxide (LYE)

• ¾ ounce Sodium Hydroxide (LYE)
• ½ cup Water

Put the water in a glass jar that has a close-fitting lid. Slowly add the Sodium Hydroxide while stirring. The Solution may get quite hot. This is a strong alkali and should be handled very carefully. Close and label the jar. This can be kept indefinitely but should be clearly marked. If any gets on your skin, wash with lots of water.

Solution Two: Sodium Hydrosulfite

• 2.5-ounce Sodium Hydrosulfite, and 1-pint water
• or ¾ ounce Thio-Urea Dioxide (also called Spectralite), and 1-pint water

Put the water in a quart jar. Add the Hydrosulfite (or Thio-Urea. Stir gently to dissolve. Hydrosulfite will generate an unpleasant odour, and will keep for a few days only; the Thio-Urea should be good for several weeks. Close up and label the jar.

Solution Three: Indigo Stock Solution

• 1-ounce Indigo
• ½ cup of Solution 1
• ½ cup of Solution 2

In a glass or enamel pan, stir one-ounce Indigo Powder into ½ cup water, until thoroughly moistened. Stir in ½ cup of Solution 1. Dilute to one quart with water (add about three cups of water); and heat to 120°-130° F (never above 140° F). Add ½ cup Solution 2, and let stand 30 minutes. At this point, you should see a yellowish solution beneath the blue surface (Indigo on the surface will oxidize back to the blue insoluble form). A drop of this solution running down a glass surface should turn blue in 20-30 seconds.

PREPARE THE DYE VAT:

• 1 oz of Indigo Stock (Solution 3)
• 2 oz of Sodium Hydrosulfite Solution (Solution 2)

In your large enamel dye pot, heat 2–3-gallon water to 120° F. Add 2 ounce (about 4 tablespoons) of Solution 2. Let stand 10 minutes. Then add 1 ounce (2 tablespoons) of Indigo Stock Solution. Let stand 30 minutes.

This should be clear and yellowish and is now ready for use. Enter the washed, wet fibre (preferably soaked overnight). Avoid making bubbles, and stir only enough to submerge the fibre. After 30 minutes–with occasional light stirring–lift the fibre out without squeezing and allow to oxidize (hang it up) for another 30 minutes. Repeat this dipping and airing pattern until the desired depth of colour is reached.

Add more Indigo Stock Solution–2 ounces at a time–as needed for colour. If you are dyeing large skeins (4 ounces or more), use 4 ounces of Stock Solution so that the dyebath won’t be depleted as rapidly. If the dyebath turns blue, add another 2 ounces of Solution Two and allow to stand for 15 minutes. Always keep the dyebath at 120°-130°F. After about four additions of Indigo Stock Solution to the exhausted dyebath, the chemistry gets tired and complex. It’s simplest to start a new vat.

RINSING YOUR WORK:

When the dyeing is done, treat the fibre to neutralize any remaining alkali, and to set the dye. First rinse in lukewarm water with about one cup of vinegar added. Next rinse in cool water. Wash gently in hot soapy water. Finally, rinse in clear water.

Recipe #2: DARK BLUES WITH THE INDIGO HYDROSULFITE VAT

If you want a dark navy, use the increased-strength Stock Solution given below. Prepare Solution 1 and Solution 2 as in Recipe #1.

Concentrated Stock Solution:

• 1 oz Indigo
• 2 tablespoons of Solution 1
• 2 tablespoons of Solution 2

Stir Indigo into 2 tablespoons of water; stir in 2 tablespoons of Solution 1; dilute to one cup with water; heat to 120°-130° F; add 2 tablespoons of Solution 2.

To dye dark blue: prepare vat as before; add 3-4 tablespoons of Stock Solution; dip about ½ pound of Yarn. After every other dipping, add 3-4 tablespoons of fresh Stock Solution. You’ll have a moderately dark blue after the third dip, a very dark blue after the fourth.

Our thanks for the above Recipe to Devin McQueen, Susan Emmons, USDA Bulletin #230, Rita Adrosko’s and Violetta Thurstan’s books.

Recipe #3: INDIGO

YEAST-AMMONIA FERMENTATION METHOD

• 1 tablespoon powdered Yeast (bread yeast)
• 1 cup warm water
• 1 rounded tablespoon Sugar

Combine the above ingredients and let stand in a warm place for about 2 hours. At the same time, dissolve 2 level teaspoons of Natural Indigo in ½ cup non-sudsing Ammonia (let sit for about 2 hours).
Add the Indigo and Ammonia to the Yeast-Sugar mix in a half-gallon jar. Fill to the top with warm water, stir once, cover with plastic wrap, using a rubber band to seal. Don’t use a rigid seal, the fermentation can burst it. Let this jar sit for several days in a warm place. The liquid will clarify to an even yellow.

The Yeast has removed all the oxygen, enabling the Indigo to dissolve. If your jar stays blue, add more yeast (if this doesn’t do it, add more sugar also). When it goes yellow, immerse some pre-wetted Yarn, and leave in overnight. Remove carefully (not dripping into the jar, adding oxygen). Hang in the air for 20-30 minutes. Repeated dips will deepen the colour.

The not-very-pleasant smell will disappear from your dyed goods with the final rinse (see Rinsing, Recipe #1). With thanks to the Boston Area Spinners and Dyers, and to Fred and Willi Gerber.

Don’t be surprised with any of these Recipes if your work fails to pick up colour in the dyebath. It’s not supposed to. The Indigo colour doesn’t bloom until air (atmospheric oxygen) has worked on the Indigo infused fibre. Magical, truly it is.

Dye kits are available. The dye kit contains natural indigo, soda ash, thiourea dioxide, hide glue, and gloves and a mask.  It will dye approximately 5 pounds of material or yarns in the deepest indigo shade. In addition, you also need a small amount of sodium hydroxide (lye) to dissolve the indigo.

You need a dye kettle of Stainless steel: Stainless steel kettles are the best quality dye vessels available.  They will not alter the colour of any natural dye bath and will virtually last forever.  Choose heavy-walled stainless-steel vessels 18/10 gauge. The thin, shiny variety can leach metal which will alter the colour of your dyebath. Making the Extract Stock Solution in Preparation for Dyeing 

1. Put 2 oz. of natural indigo into a quart glass jar with a wide mouth.
2. Add 1/4 cup warm water (80° F) and stir to make a paste.
3. Add one more cup of water and stir. The solution should be opaque and blue.
4. Add two TBS of an alkali (e.g. sodium hydroxide or lye) to dissolve the indigo. Stir carefully.  Always wear gloves, mask and protective eyewear when measuring and using lye. Do not breathe the stock solution vapours after adding the lye to the jar.
5. Next, dissolve two TBS thiourea dioxide into nearly boiling water (one cup), add to the stock solution and stir until dissolved. Wear a protective mask and avoid breathing the stock solution vapours.  Add enough warm water to reach the neck of the quart jar and stir gently.
6. Allow this stock solution to sit for 15 minutes so it can dissolve and reduce. The solution will change from a dark blue to a translucent green-yellow with a coppery scum on the top. Check to see if the stock is ready by dribbling some solution on the side of a white plastic cup and note the change from a transparent green-yellow to a dark opaque blue once oxidized. 
   

This stock can be kept indefinitely if stored in a dark cool place and sealed securely. Natural indigo extract always has a distinctive grassy odour because it is often composted with local organic matter prior to exporting. If the stock turns blue over time, add a scant 1 TBS of dissolved thiourea dioxide.

Check the pH to see that the stock remains pH 11, if not add 2 tsp of lye and stir well. If some of the stock evaporates over time simply add warm water and 1 TBS of dissolved thiourea dioxide, stir well. Wait for 15 minutes until the stock once again reduces and changes colour.