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:

Broom Update

The Scotch broom (Cytisus scoparius) is gone. I appreciate all of you who warned me about the potential problem of letting it go to seed.

The dyer’s broom (Genista tinctoria) is now in full bloom and there is plenty of room for it to spread.

broom in bloom
broom in bloom
dyer's broom, detail
dyer’s broom, detail
left, cotton woven shibori with various mordants, right, wool  with alum mordant. dyed with broom
left, cotton woven shibori with various mordants                                                                                   right, wool with alum mordant                                                                                                                        dyed with broom

A Lesson About Dye Plants: Broom

Several years ago, as a novice dye gardener, I was perusing dye books to determine which plants I could grow here in the mountains of North Carolina, and I found a mention of the plant called broom. I had never grown it before and had never dyed with it, so I ordered two of the plants that were specified in the book: Cytisus scoparius, otherwise known as scotch broom. I had seen this plant growing along the roadsides in the west and knew that this plant was very invasive. Were all of those plants a potential source of great color?

After the plant had been in the ground for a year, I did more investigation and learned that scotch broom (Cytisus scoparius) was NOT the great dye plant I thought it might be. The one I should have planted was dyer’s broom, (Genista tinctoria). Other names for this dye plant are dyer’s greenwood or woad waxen. It has a long and distinguished history as a plant used for dyeing. In fact the word “tinctoria” is the latin word meaning “used for dyeing” and any plant that has “tinctoria” in its name has been traditionally used for dyeing. All dye plants, though, do not contain the word “tinctoria” in their name.

I ordered two dyer’s broom (Genista tinctoria)  plants and put them into the bed outside my studio next to to the scotch broom. When both plants were large enough I did some dyeing and compared the samples. I needed to see for myself what, if any,  difference there was in the two plants. There was clearly “no contest” in the results obtained The dyer’s broom dyed both wool and cotton in brilliant yellows and yellow greens. The color is  very similar to the one I get from weld plants. In fact both weld (Reseda luteola) and dyer’s broom (Genista tinctoria) contain luteolin, which gives a clear yellow that is extremely fast to washing and light. The scotch broom (Cytisus scorpius) gave me a very pale yellow or beige color.

The scotch broom (Cytisus scoparius) in my garden is blooming this spring for the last time. As soon as the flower “show” is over I plan to  remove it in order to make additional room for the dyer’s broom (Genista tinctoria).

Last year I was able to harvest enough of the dyer’s broom (genista tinctoria) for several projects and dry some of the shoots and leaves for later use. Genista tinctoria has earned a place in my garden. I still have a lot to learn from this plant, such as when is the best time to harvest for dyeing or drying and how to keep it pruned properly. I have learned to do more research about my plants and ALWAYS to pay attention and use their latin or scientific names.

Cytisus scoparius, left Genista tinctoria, right
Cytisus scoparius, left. Genista tinctoria, right