Hints & Tips for Natural Dyers: How to Minimize Indigo Crocking

Preparing the indigo vat

1. It’s supposed to rub off. That’s why blue jeans fade.

2. Certain cultures attribute indigo crocking to its authenticity and prize the way that excess indigo comes off on the hands or body. I found a description from Duncan Clarke  of Adire African Textiles on how West African cultures dye and prepare indigo cloth:
After the dyed cloth had dried it was customary to beat the fabric repeatedly with wooden beaters, which both pressed the fabric and imparted a shiny glaze. In some areas additional indigo paste was beaten into the cloth at this stage, subsequently rubbing off on the skin of the wearer in a much desired effect.”

3. Okay, we are not that culture. If you dip in a well-prepared vat with clean fibers and oxidize in a hydrogen peroxide bath afterwards, you should be able to minimize crocking.

Minimizing Indigo Crocking on Yarns and Fibers

Some observations
* Indigo on cellulose and bast fibers such as cotton, linen and hemp appear to crock less
* Indigo dyed fibers that will later be spun seem to crock more.
* Indigo dyed on dirty or greasy fiber will not bond well and will rub off.
* Something that is dipped incorrectly in the first place will crock forever (or show other signs of stress like streaking, premature fading or yellowing).
* Some indigo powders are filtered more than others resulting in a purer vat and better adhesion of the indigo to the fibers.
* The rest of this post assumes you are familiar with creating an indigo vat using either a stock solution or the Botanical Colors method using the weight of fiber and that you know what a correctly reduced vat looks like.
* We’re calling the creation of the stock or the paste the indigo “mother” (a term that I learned from Denise Lambert of Bleu de Lectoure).

-Indigo needs a bit of time to adhere to the fibers. A two or three second dip will often result in streaky indigo that crocks. It’s better to create a very weak vat and let your fiber stay in it for a longer period of time than it is to dip quickly.
-If there’s a lot of sediment at the bottom of your vat, keep the goods away from this deposit.
-A very old and overused vat can be bad news. It’s filled with sludge, dye runoff and probably a bit too much reducing agent and is quite temperamental and can go off balance very quickly. It’s better to start with a fresh vat if you are working on a tricky color.

Step 1 – Balance your vat correctly
A correctly balanced vat is the first line of defense against crocking. Indigo needs an alkaline and reduced environment in order to bond securely with the fiber. Too low of a pH and the indigo doesn’t completely dissolve. Too little reducing agent and the indigo will rub off. Too much reducing agent and the vat will strip away the deposited indigo, yielding a lighter color. Are you feeling like Goldilocks checking out the indigo vats? It’s important to review your indigo technique and make sure you have a balanced vat when you start dipping and that you keep rebalancing it throughout your indigo session.

In order to maintain consistency when balancing a vat, here are the steps I take when I create a vat.

-Add the prepared indigo “mother” to the water in your vat. Heat the vat to about 100-120F.
-Measure and adjust the pH of the vat. Add dissolved soda ash to the vat until the pH is 10.
-Wait for 15-20 minutes. The thiourea dioxide or sodium hydrosulfite used to create your indigo “mother” is often enough to reduce the vat with the addition of a little heat.
-If the vat is still under-reduced (blue or dark green) after 20 minutes, then add a **small** amount of dissolved thiourea dioxide or sodium hydrosulfite and wait 15 more minutes.
-Once the vat shows the correct greenish yellow clear color, then carefully add dissolved Hide Glue (for protein fibers only) and start dipping.

Step 2 – Oxidizing

I oxidize in a water bath that contains hydrogen peroxide and a small amount of soda ash. If I am dipping protein fibers, I often omit the soda ash. The hydrogen peroxide speeds up oxidation and seems to “clean” the dyed fibers so there is subsequently very little wash out and I’ve found that I have very little crocking.

-Use 1 pint of 3% hydrogen peroxide(the kind that comes from the pharmacy) per pound of fiber being dipped. Mix in a 5 gallon bucket of cool water. Dissolve 1% soda ash on weight of the fiber and add to the bucket of water.You can use this mixture for the day’s indigo dips.
-Immerse your yarn or fiber or cloth in this mixture after removing the goods from the indigo vat for 15 minutes. You can let the excess indigo drip into another catch basin first if you wish.
-Remove the goods from the hydrogen peroxide bath and allow the goods to continue to oxidize for 30 more minutes.
-Repeat the dips until your fibers are the desired color.

Step 3 – Neutralizing
-Neutralize the dyed fibers in a second bath that contains 5% acetic acid on the wof and let soak for 30-45 minutes.
-Remove and rinse in cool water. The rinse water should run clear after two or three rinses.
-Let the fibers dry out of the sun.