The Effect of pH on Yellow Dyes from the Garden

yellows on line

First of all, I know that my well water is acidic. It measures about pH 6.0 here in the mountains of North Carolina.  The water is ideal for most dyeing. There is no iron or other minerals that might dull the colors. The acidity is another issue. 

Most of the yellow dyes in my garden, or those that I might gather locally, are flavonoids. That means that they require a mordant in order to attach to the textile. No mordant means no yellow. It’s that simple. Some of the dyes may also contain some tannin or other colorants but the yellow is what we’re talking about here. 

Last summer Joy Boutrup and I taught a class together at Penland School of Crafts, located near my home in western North Carolina. A student in the class was especially interested in gathering local plants for use as a dye source. She struggled to get the locally gathered dyes to attach to her textiles, especially onto mordanted cotton. 

Joy had the answer-of course!

When the dye meets the mordant in a textile, an insoluble lake is formed. This lake is formed most readily in neutral or slightly alkaline conditions.

An alum mordant makes a very strong bond with wool but there is no chemical bond between cellulose and the mordant.  Instead, the mordant is deposited as an insoluble compound on the textile.

An additional issue is that many of our local plants are acidic. When the plants are boiled in our already acidic water, the pH of the dyebath becomes so low that the dye may struggle to attach to the mordant in the fiber. In fact, the mordant in the cotton can be damaged or even removed if the bath is acidic enough. This is exactly the reason why we don’t add an acid to a cochineal bath when dyeing cellulose. The mordant would be damaged and little dye attaches. 

The remedy: Add a small amount of chalk (calcium carbonate) to the dye bath to neutralize the acid that is present. This will do no damage to the dye or the textile. Chalk is not an alkaline but will neutralize an acid that is present. Within reason, there is no possibility of having too much chalk and any excess will simply precipitate in the bath and rinse out of the fabric

Since my own broom (Genista tinctoria) is currently in need of a serious trim, I began a series of flavonoid dye tests with that and then compared other dyes from my garden and environs. 

I used all fresh plants at 300% w.o.f. and dyed both wool and cotton. The wool was mordanted in alum. The cotton was mordanted using tannin plus alum and soda ash. After making the dye decoction, I divided the dye bath in two equal portions and added both wool and cotton to each bath.  Chalk was added to only one of the baths.

The results were quite surprising (but also very consistent) and made me realize that I have likely not been achieving the maximum amount of color from some of my local dyes. 

The plants I gathered and used were

    • Broom (Genista tinctoria)
    • Wild grape leaves
    • Apple leaves
    • Dyer’s Chamomile (Anthemis tinctoria). I used the flowers and after gathering a basket of the small flowers I tested the dye content in the entire plant. 
    • Staghorn sumac (Rhus typhena) . We often think of sumac as a good source of tannin but the leaves, according to Dominique Cardon, are also rich in flavonoids. 
    • Weld (Reseda luteola). This is my “go-to” yellow dye. I almost always use dried plants and I rarely add chalk with weld on cotton but frequently  add it to a wool bath. 

After boiling the plant material I recorded the pH of the decoction. The pH was measured again after the addition of chalk. Each dye bath was approximately 4 liters and I added about 1 TBS of chalk. 

The chalk will alter the appearance of the bath from transparent to cloudy and nearly opaque. 

weld in pot w/wo chalk
Weld baths: no chalk on left, chalk added on right
plant pH after boiling pH after addition of chalk
Dyer’s broom 

(Genista tinctoria)

5 6
Wild grape leaves 4 6
Apple leaves 5 6.5
Dyer’s chamomile (Anthemis tinctoria) (flowers) 4.5 6.5
Dyer’s chamomile (Anthemis tinctoria) (whole plant) 4.5 6.5
Staghorn sumac (Rhus typhena) 4 6
Weld (fresh plant) (Reseda luteola) 5.5 6.5
Weld (dried plant) 5.5 6.5

The samples below are wool. Individual samples on the left had chalk added to the bath. Those on the right did not.

In every case, I achieved  deeper and brighter yellows colors when the chalk was added to the fresh plant baths. The only exception was dried weld, which was used at 50% w.o.f. When dyeing with the fresh weld plants, deeper yellow hues resulted with the addition of chalk. When I used dried weld plants, the chalk made very little difference.  I asked Joy about this and she indicated that is was possible that some of the acids disappear in the drying process. It will require more tests and explorations to confirm this.

The cellulose samples are especially notable. The high acidity of some baths made without the chalk was enough to damage the mordant significantly. The grape leaves and the sumac, which were the most acidic, destroyed the mordant in the cellulose and only the tannins that are present in the leaf were able to attach and color the fabric. 

cellulose no chalk
Palette of color on cotton without the addition of  chalk.  Left to right: Chamomile flowers, broom, apple leaves, chamomile (whole plant), weld, sumac, grape leaves
cellulose with chalk
Palette of color on cotton with the use of chalk.  Left to right: Chamomile flowers, broom, apple leaves, chamomile (whole plant), weld, sumac, grape leaves

If your water is not acidic, or has calcium in it, then these tests may not be relevant but the addition of chalk will never harm the fiber or the dye and may release more color.

I recently found the following note that I had made during a class with Michel Garcia several years ago referring to grape leaves:

“If they are too sour they will dissolve part of the mordant.”       M. Garcia

 My own notes continue to say:

After boiling the grape leaves the solution of a pH 4 – too acidic – it will remove the mordants. Sumac will cause the same effect. Boiling breaks the bonds of the tannins and gallic acid is released. Add chalk to the bath to decrease the acidity of the dye bath – you cannot be in excess of chalk.

Sometimes we’re just not ready to absorb information the first time we hear it. This is exactly why I continue to question, keep notes, and actively test and observe. 

It’s summertime! Enjoy your yellow flavonoids!

Note: I purchase my chalk from a potter’s supply store. It is inexpensive and can be purchased in quantity. Potters refer to it a “whiting” and rarely refer to it as chalk or calcium carbonate. Do check the MSDS though, just to be sure. 

Upcoming: On July 13 I am presenting a Zoom webinar, entitled Colors from the Garden, as part of the John C. Campbell Folks School’s Appalachian Traditions Series. You can sign up here:

22 thoughts on “The Effect of pH on Yellow Dyes from the Garden

  1. Hi Catherine,I have alot of dye plants growing. Our water is neutral. Would you still add chalk ? I got good yellow but soft with rhubarb leaves, a brighter yellow with comfrey, a light but nice tan with nettles,i am cooking staghorn sumach now, next week weld. I just experimented with adding tartaric acid to the alum mordant. What do you think about that. I used an old dye book years ago by Alma Lesch and she put tartaric acic and glaubers salts with every alum mordant pot. I don’t know if I told you but I lost my husband last year in late August. He was my partner in everything. I don’t know if classes will be possible in the future. I am still very commited to natural dyeing,Best,Sara Burnett

    Sent from Frontier Yahoo Mail for iPhone

    1. Hi Sara, I certainly will not hesitate to try the chalk and see if it has any effect. You can’t harm anything. Some of the plants are acidic, so it could make a difference. So sorry to hear about your husband…

  2. Wonderful testing and information once again. I so look forward to your posts and instructions re testing and experimentation. What a difference the chalk makes! Isn’t nature exquisite. Thank you.

  3. Hi Thank you for your excellent blog. I have a question regarding this; How is chalk not an alkaline? It has a ph of 7.5, or am I misunderstanding it?

    Regards, Suzanne

    On Tue, 23 Jun 2020 at 23:53 Natural Dye: Experiments and Results wrote:

    > Catharine Ellis posted: ” First of all, I know that my well water is > acidic. It measures about pH 6.0 here in the mountains of North Carolina. > The water is ideal for most dyeing. There is no iron or other minerals that > might dull the colors. The acidity is another issue” >

    1. Chalk can have an alkaline effect on soil, water, etc but it is so mild – nothing like the aggressively alkaline soda ash or even baking soda. It would be possible to use soda ash for the same effect but you would have to be so very, very careful about the amount added and even a small amount could make the dye bath too alkaline. The main effect of chalk is simply to neutralize the acid. and we also use it to neutralize mordants that are used for printing.

      1. I have been routinely adding a pinch of soda ash to my weld when I paste it up–and nearly the same amount (maybe a bit more) of calc carb. I don’t hate my results: acid yellow in an emersion bath and a more mellow medium lemon yellow with alum mordant printing. But should I not be adding the SASH at all? It was suggested to me to add it, is why I do, but I’m not married to it. 🙂

      2. I’ve never heard of adding soda ash, but very tiny amounts would accomplish the same thing. The problem with using soda ash vs. chalk, is that soda is is an alkaline and it would be so easy to use too much.

  4. What fabulous experiments. Please may I ask which parts of the genista you used? I am following your recipe to make pigments, so far I have both yellow and blue from my woad plants, but I while I was able to get both green and pink from the woad flowers, leaves and seeds on wool, nothing precipitated. This morning I am trying with coreopsis petals. (Ps, love your book)

  5. This is why I always chalk/dung my cellulose, regardless of the mordant method used, since it neutralizes the fibre pH and aids maximum dye uptake. Your excellent blog posts always get the wheels turning. It would be interesting to test dunged cellulose vs. un-dunged cellulose, and half of each in a chalked dye bath and the other half in an un-chalked dye bath, to see what effect chalking the fibres has vs. chalking the dye bath, and the combined effect of both. Some flavonoids are also acidic, themselves, so I wonder what effect neutralizing bath pH would have on their molecular stability and ability to bond with mordanted fibres. Thanks so much for sharing your tests.

    1. When using the calcium carbonate after the mordant, does it need to be warmed up each time a fabric is soaked?

  6. I signed up for the webinar, but I will have to furtively watch it as I will be at work. Will it be recorded for viewing later?

  7. Thank you so much for this post. So much food for thought. Will now give this a trial here in Australia with my cellulose work.

  8. Thankyou for sharing these beautiful results. What an incredible difference with a little chalk added to harden the water in the dyebath. Beautiful colour with the dyers chamomile, hope to try this too with tiny linen samples. I read an interesting article ‘A Grass that Grows in Bologna’ about medieval weld dyeing. Mentions alkalinity and takes it a little further into the alkaline range. I tried it with fresh weld recently, vibrant saturated yellow on cotton. Water here in Edinburgh is soft and neutral so I added chalk and then a tiny bit of washing soda towards the end of gentle heating.

    1. You are the second person to mention washing soda, which I have never used with weld. But I think we’re all talking about the same issue. Nice to know there is more than one way to fix that acidic water and get the most out of the dye.

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