Oh, Shift! Using pH Adjustments to Extract Pigment and Modify Colors From Madder
Some natural dyes are more sensitive than other to changes in pH. Both species of madder that I have been using recently, Rubia cordifolia and Rubia tinctoria (or tinctorum) fall into that category. In this post, I am specifically talking about Rubia cordifolia (RC), which is the species that grows in India and is widely used around the world today, though its historic uses stem from India, Africa, and, later, Europe. I started out with two different batches of RC. One appeared a golden yellow, almost like turmeric, when it arrived. The other appears more of a dark terra cotta color. Since the yellow one was already opened for a previous batch, I started there, and the results have been amazing! All of the examples in this post were dyed in the same batch of dye, though I refreshed it several times as it became exhausted, meaning it’s running out of pigment. Each refresh was done with the same “log” of material, which has so far yielded 4 large pots of gorgeous color, and it is not quite exhausted yet!
I started with 50% of the weight of fiber I planned to dye: 8 ounces of madder for a planned pound of fabric. I have now dyed more than twice that amount of fiber. Clearly, I could have used less material (the normal range for madder is 25% to 200% W.O.F.), but when you use less material, it can take a lot longer to get it extracted and concentrated enough to make good dye, and a less concentrated dye bath takes longer to deposit enough color on your fiber. I’ll discuss that point more later. My choice is to stick with more plant material, and re-use it more times.
Extracting pigment from Rubia cordifolia
Different natural dye plants contain different pigments, and there are different processes to extract the pigment from the plant material without damaging it or shifting the color to an undesirable hue. For the purpose of dyeing, we use the roots of the madder plants. The primary pigment found in RC is called munjistin, and it also contains purpurin pigment. Because RC has been used to dye textiles since ancient times and continues to be used in commercial dyeing today, people have developed a wide range of processes to extract the color in a way that makes strong and pleasing dye. Commercial processes tend to focus on cost, speed, and repeatable results, and they use chemicals like hydrochloric acid and toluene, which most natural dyers won’t want to deal with.
The extraction method you choose will ultimately depend on what color you want as a result, and what type of fiber you plan to dye. I’ve tried many methods from historical sources and modern ones, and am always experimenting with more, but in my opinion, the most versatile and beautiful process for extracting RC is to use an acidified bath for extraction, then adjust the pH of the bath after extraction and before dyeing. I use citrus as an acid source. Vinegar is also a great acid source because it’s inexpensive and non-toxic. It just happens that I have a nearly endless source of free citrus and I prefer the scent over vinegar, so I use lime or lemon juice, or a solution made with dried citrus peels. Lime juice is the most acidic, and gives results with the lowest volume of added material. Lemon juice gets the job done, but it takes about twice as much of it to achieve the same result as lime juice. The peels (orange, lemon, lime, grapefruit, or a blend) are far less potent, but we have so very many of them and I hate to see them go to waste, so I figured out how to “brew” the dried peels to make an acidic solution. Lime juice is my first choice, but it’s nice to know that I always have backup if I need it!
My preference is not to dump natural dye plant matter straight into the water. Other dyers do this, and it will usually work just fine, but it’s also a lot more work to wash out later, especially if you’re dyeing yarn or highly textured fabric. Depending on the texture of the dye material and the amount I need to use, I might put the plant matter in a mesh bra-washing bag, a cotton muslin bag, or roll it into a cheesecloth log, secured with cotton thread or rubber bands. In this case, the RC I had was powdered, so I put the powder into coffee filters, which I burrito-folded, then put those into the cheesecloth and tied it into a log. Let me pass along a bit of knowledge I earned the hard way: don’t pack your dye material too tightly, or it will take forever to get saturated and start releasing pigment.
Adjusting pH for desired color
Those of you who have taken classes from me or know me personally know that I despise waste and am always looking for ways to use things that would normally go to waste. Sadly, in the case of madder, I have found that the generations of dyers who came before were absolutely right on one point that brings me pain: You need to throw out the first pot of dye that you make from a new “log” of madder, then use the same log of madder to make subsequent pots. The first colors that come out of the madder as it gets saturated is ugly, brown, and weak. I have done a great deal of experimentation to find a way to make this first batch useful (I’ve tried concentrating it, blending it with other dyes, shifted the pH every which way), but in every case, I knew another dye material and process to get the similar or better results with much less work and fuel cost.
So, starting with the second batch, I got a dense orangey-yellow from my RC log. It looks more orange in the photos and video than it did in person. Because I wanted to show examples of the color variations, I did something I normally wouldn’t: I dyed both cotton and silk in the acidified dye bath, which yielded a lovely assortment of yellow, orange, and peach colors.
The two narrower pieces in front are silk. The one on the left was mordanted in titanium oxalate (TO), and the one on the right was mordanted in alum. The lighter cotton piece directly behind the silks was mordanted in alum and given a chalk bath, but left in the dye bath for a much shorter time. The three cotton pieces at the back were all mordanted in alum, each in a different tannin, then a second alum and a chalk bath immediately before dyeing.
One reason I opt for using a greater W.O.F. percentage of dye material is that a more concentrated bath lets you dye your fiber more quickly, so you can do things like dye cotton in an acidified bath or silk in a more alkaline bath without ruining the fiber.
After I dyed my examples in the acidified bath, I was a little worried that I’d used up too much of the pigment because I got a little carried away (this is only one rack of what I did, because I wanted to demonstrate another point about pH shifting later), but my fears were unfounded. This champion of a pot had plenty of pigment left to make a gorgeous demonstration of the pH shifting process and several pieces of glorious pinks. I used soda ash to raise the pH, and I remembered to shoot video so you could see the cool transition: pH Shift Video
The resulting dye gave a range of pinks and coral on cotton and silk, all mordanted in the same way as the previous examples. The smaller items in a deeper color at the left are fingerless gloves made of cotton knit, mordanted in alum and given a chalk bath. They soaked up the dye quite efficiently!
The right-hand photo shows a weird example I did to show the difference between acidified (top) and pH-shifted (bottom) RC dye. I was pretty sure the colors would level off in the finishing bath, which they did (the scarf is now all one color). I love the purple stripe where the two different pH levels met. I’ll talk about finishing baths shortly, but in relation to this example, I will say that I could have finished this piece in a way that maintained the color difference, but it would have been a lot of work for a piece that I kind of threw together on a whim. Apparently, I forgot to take a picture of the final version, but it is a solid color which is closer to the bottom pink than the top peach. I’d call the final color a medium coral, which is quite pleasing, and will look lovely with some resist work and additional dyeing. It would be a striking contrast with walnut overdye, or it would create a subtly beautiful pattern with a more closely related shade, like another variation on madder.
Sound the (re)charge!
Since I set out to make colors in the red family with this pot, I could see that it was going to need a re-charge before going on. I had already color-shifted the pot of dye, and I didn’t want to stop the chemical reaction that was extracting the pigment from the madder log, so simply dropping the log back into the pot of dye was not an option. I started a second, smaller pot of acidified water and extracted more pigment from the log, then added that water to the dye pot and re-adjusted the pH so it was the same as the previous day’s dye that produced the pinks. I was very happy with the results, which range from cherry red to almost burgundy.
In the right-hand photo above, all of the items are silk mordanted in alum, except the widest one in the middle, which is extremely thick cotton, originally intended as an obi liner. This piece was mordanted in alum, Aleppo oak tannin, then alum again (ATA), and given a chalk bath before dyeing.
The left and center photos show the same cotton handkerchief. The left picture is how it looked after dyeing, rinsing, and drying. The center photo shows how the color looked after the final bath. I do a final bath on all of my natural dye pieces. For dyes that are not pH sensitive, I will use water and a small amount of Orvus soap, which is very close to pH neutral.
For pH-sensitive dyes like madder, the final bath takes a little consideration because it can change your final color in unwanted ways if you’re not careful. If you’ve shifted your dye pot significantly off of neutral, you need to make a final bath that supports that shift, rather than leveling it to neutral. If you’ve dyed in an acidic bath and you intend to keep the color that resulted from that shift, you need to acidify your final bath. If you have a color you love that resulted from high alkalinity, you need to raise the pH in your finishing bath, too.
That also means you need to plan what colors you apply to different fibers carefully. Remember the examples above where I dyed cotton in the acidified madder? I knew when I did it that I couldn’t leave it that way, because cotton fiber breaks down with prolonged exposure to acid. On the other side of the coin, protein fibers like silk won’t tolerate prolonged exposure to high pH. I can dye silk or wool in an alkaline dye bath to get the beautiful red, but I also have to keep in mind that my finishing bath needs to be neutral, or the fiber will be damaged over time. With experience, you learn to plan for these factors. While you’re learning, you will surely get some surprise results. Even with experience, there is always that x-factor in natural dyeing waiting to throw in a few surprises along the way!
