Indigo and Crocking

At this time last year, The Art and Science of Natural Dyes (Schiffer Press) was published. Joy Boutrup, my co-author, and I submitted the completed manuscript almost two years ago. During these last 24 months I have been teaching, traveling, and continuing to work in the studio. We have heard from many of you and appreciate that dyers are actively using the book. I’ve tried to respond to the numerous questions and comments that have come my way. 

I continue to learn, and plan to publish a series of posts that will reflect some of the lessons from the dye studio that have revealed themselves in the last months. 

Today I want to share issues with indigo and crocking. 

A couple of years ago, I took up knitting…once again. I dyed yarns in my 30 gallon indigo vat reduced with henna. This vat has been dyeing well for approximately 3 years.  I came directly in contact (no joke) with the crocking issues of indigo. Crocking occurs when excess dye rubs off onto another textile or on the skin.  My knitting yarns had been dyed well, neutralized, finished by boiling and yet still they crocked. Because of the handling of the yarns, knitting reveals rubbing issues that are easier to ignore with other dyeing projects. 


crocking indigo
Testing for crocking is done by rubbing a small piece of white cotton 30x onto the textile.

This has started me on a long, involved exploration of indigo vats that has taken me in many directions. 

Indigo does not attach to the textile in the same manner as mordant dyes, so I think that some crocking is inevitable when dyeing with indigo but I wanted to see if we could decrease the amount of crocking on my yarns. 

I suspected that part of the problem was the high quantity of lime (calcium hydroxide) in the henna vat – or in any of the quick reduction vats. Joy also believed that the calcium binds to the indigo, making it more difficult to remove from the textile. 

The first thing we explored was a more thorough washing of the dyed textile.  Usually I finish all textile with a neutral detergent but a mild alkaline soap is particularly effective in removing excess dye. In order to be effective, the soap must be concentrated enough to foam up when heated. We soaked the indigo dyed textile in a mild “Ivory Soap” solution. We watched and saw that more of the excess indigo released from the textile in the soap solution than with a neutral detergent. The challenge when using soap is that it does not rinse out, leaving a fatty substance behind that would make mordanting and over-dyeing problematic. We used a heated Metaphos (phosphate) solution to remove the soap. But we saw no difference in the crocking after this treatment. 

soak and rinse water
soaking water with detergent (left) and soap (right)

Next, we experimented with substituting lye (sodium hydroxide) for the lime (calcium hydroxide) in both henna and iron vats. Joy determined the amount the lye required, based on the molecular weight. We substituted 1.3 grams of lye (sodium hydroxide) for 1 gram of lime (calcium hydroxide). 

We often think of lime as being benign because it can be purchased it in the grocery store as “pickling lime” but it is a very strong alkaline and we need to be careful with both of these substances.

While teaching at Penland School of Crafts last summer, Joy and I made two 5 gallon vats with the class, using lye with  henna and iron as reduction agents. Initially these vats worked very well and there was an added benefit with the lye: no calcium sludge in the bottom of the vat.

henna lye vat
“Rubbing cloths” indicated by dotted lines. The henna vat made with lye resulted in excellent rub-fastness.

 The vats made with lye seemed to significantly decrease the amount of crocking but I did find the these vats more challenging to keep in reduction for long periods of time than those made with lime. The pH had to be watched more carefully, as the henna vat would go out of reduction when the pH went below 12 and required boosting with more alkaline.  I do believe there is potential to make these “lye” vats work well, but my own follow-up experiments were done with small 2 liter vats and I never scaled these vats up. The truth is, I got distracted by fermentation vats, which have long been on my own list to explore. 

In my next post I will share some of what I have learned about fermentation vats. 

Coming up: The North Carolina Arboretum will host the third Growing Color Symposium in Asheville March 11 & 12, 2020. Presenters include Sally Fox, Sara Bellos, Donna Hardy, Rowland Ricketts, Dede Styles, and myself. Rowland and I will teach a workshop on the indigo vat and Sarah Bellos will be able to update us on Stoney Creek Colors and their indigo harvest and extraction. Donna Hardy will also do a post symposium workshop at Cloth Fiber Workshop. Do come if you can! 

22 thoughts on “Indigo and Crocking

  1. Catharine I have been meaning to congratulate you and Joy on your excellent publication! Clear, well written, informative and very useful in the studio. Such a good contribution to the natural dye knowledge sharing scene!

  2. Lovely to see this pop up! I also have been slowly coming to the the conclusion that the 1-2-3 formula is more lime than needed for a henna vat, and that the extra may be causing problems … I’ve been experimenting with using less lime, and trying to encourage more fermentation … now I’m looking forward to reading the next part!

  3. Catherine, have you explored vinegar rinses to remove the lime? I’ve been using it to clean my indigo extracts. I have also used it to neutralize for silk & wool. I wonder if you make it part of the process of rinsing & layering if it would minimize clocking.

  4. I’ve always used vinegar to neutralize. That’s what makes me think it’s something different. It’s not just the alkalinity but the indigo is actually binding to the lime. When the lime is in excess, then it becomes a problem. Last year, when I was in Okinawa, I heard about too much lime begin used in the water extraction process. The excess of lime meant that there was very little indigo left in the paste. I wish I understood all of this from a molecular level but only know what I observe and experience.

  5. Hello Catherine, Thanks for this very interesting post. I work with wool mainly. I put my hanks straight from the indigo vat into a bucket of water ( as much as possible the same temp as the vat but I guess with cellulose that would not be necessary ) I leave the wool to oxygenate there for 5 mins. or so and then finish it off in the air before re-dipping it in the vat.
    At the end of the dyeing day I put the bucket of water, which is usually but not always, very blue back into the vat. I find this prevents crocking , it seems to be a combination of slow oxygenation and rinsing off the non attached indigo before it starts piling up and we get indigo adhering to indigo.

    I also work from observation and experience, wouldn’t know what a molecule looks like!

    1. Thanks for this, Andie. I also put my textiles into water immediately after dyeing but only for a quick rinse before oxidizing fully in the air. This would be easy to try. What kind of vat/reduction are you using?

  6. Thank you for your book and your blog. I’m a novice indigo dyer so had assumed this issue was all about my inexperience and limited skill. I eventually tried soaking the yarn in soymilk (after all the steps you mention in rinsing, washing and neutralisation) and I think that did help…! I am so impressed with your thoroughness. Thank you for sharing your findings.

  7. Dear Catharine, I am actually working with a henna / dates vat using less lime, a recipe passed by David Santandreu : 1 part indigo, 3 parts henna (infused leaves) , 1 part date (made into syrup ), 1 part lime. So it is a 1-1-4 recipe. The t° and ph have to be closely checked to maintain the vat active.
    Supposed to be the traditionnal Maghreb henna vat. Works well and leaves the fabric soft and beautiful. But I have not practiced this recipe enough yet to know if a crocking problem could occurs.
    hank you and Ooy for your book, clear, and well documented, a must have in the dyer’s studio

  8. Had thought this way of reducing was fermentation vat. Guess I jumped to conclusions. Thank you for so much inspiring info. Catherine de robert, do you make a tea with the henna leaves?

  9. Hi Catharine —

    I just read this blog and wanted to weigh in on the crocking issue. I have been dyeing with indigo using a traditional sig (urine) fermentation vat — I find that I get the richest blues using that method of dyeing. The fiber (I “dye in the wool” using washed but otherwise unprocessed sheep fleece) is often left in the vat for weeks at a time (a method I’ve observed in traditional cultures in Asia and Latin America). The resulting blues are very deep and the color is totally wash fast — soaking for over an hour results in clear water. But the color does crock onto hands (and hand cards, and spindles) while being processed.

    The sig vat is composed entirely of stale urine and indigo powder — the fiber is even soaked in urine to wet it before dyeing. Feeding the vat consists of adding more urine or more indigo powder.

    I’m not sure how these results relate to your research, but you might be able to use this information if you don’t want to try the (rather odorous!) sig vat yourself. Although I highly recommend experimenting with a sig vat just for the amazing color you get from it! (and the smell in the fiber goes away after washing and airing for a few days!)

    1. I’ve been reading about the urine vats and am intrigued by the fact that the urine is both the source of the bacteria and the alkalinity. I think I’m about ready to try it. I’ll start with a small sample vat. Thanks!

  10. In relation to all this, I have been reading reviews of pH meters, and am willing to spend a bit on one, since my pH papers are on the crude side. Does anyone have any suggestions for good reliable models? Not looking in the $800 range, but willing to go above $19.00. many thanks!

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