(And why do you need to know?)
pH is something you will see a lot in descriptions of natural dyeing processes. In short: pH stands for
potential hydrogen,
and it tells us how much hydrogen there is in liquids, and how active the hydrogen ion is. That concentration of hydrogen ions is measured in moles per cubic decimetre of solution.
The range of pH is from 0-14.
A pH of 7 is considered neutral, while pH values below 7 are acidic and pH values above 7 are alkaline.
The pH scale is logarithmic, which means that a change of one pH unit represents a tenfold change in acidity or alkalinity.
For example, a solution with a pH of 4 is ten times more acidic than a solution with a pH of 5, and one hundred times more acidic than a solution with a pH of 6. Similarly, a solution with a pH of 9 is ten times more alkaline than a solution with a pH of 8, and one hundred times more alkaline than a solution with a pH of 7.
How can I tell the pH level of my dye solution?
To assess the pH of a solution, you can use a digital pH meter or pH indicator strips (litmus strips) that change color based on the pH of the solution. Once you know the pH of the solution, you can make adjustments to the pH by adding an acidic or alkaline substance.
Fun fact: did you know that the traditional dyers in 18th century France would tell the right pH of their indigo vat by tasting it?
Fun fact: 'things are going sour' relates to the natural drop in pH when organic materials hydrolyze. In dye baths there will always be a natural drop in pH as the plant materials in the water naturally rot, creating a sour environment.
Why is knowing the pH level of your dye bath important?
Most natural dyes are sensitive to pH changes and will produce different colors depending on the acidity or alkalinity of the dye bath.
Madder root dye will produce a red color in an alkaline solution (pH 9-10) and a yellow color in an acidic solution (pH 4-5).
Cochineal dye is a fuchsia color on fabric with a neutral pH, an acidic of 5 can pull the shade towards reds, while pH 8 and up gives purple hues.
Most yellow dyes from flavonoids will give a more pronounced yellow in an alkaline bath.
While I was traveling in Oaxaca, we saw how the women dye their wool in a wide range of hues with cochineal, just by adjusting the pH level of their dye bath.
Can I change the pH level of my dye solution?
If you have a solution with a pH of 5 and you want to make it more acidic, you could add an acidic substance such as vinegar to lower the pH by one unit to a pH of 4. Alternatively, if you have a solution with a pH of 5 and you want to make it more alkaline, you could add an alkaline substance such as baking soda to raise the pH by one unit to a pH of 6. We call these alkaline or acidic substances an assist (see this blog)
It's important to note that too much acidity or alkalinity can damage the fibers, so it's important to follow recommended pH ranges for each dye and fiber type.
In this sample, you see the difference up close of cochineal fibers with different assists:
What makes something an acidic assist?
Acidic substances are substances that have a pH value below 7 on the pH scale, which means they are more acidic than a neutral solution (pH 7). These substances have a higher concentration of hydrogen ions (H+) than hydroxide ions (OH-).
Acidic substances can be either natural or synthetic. Some common examples of acidic assists used in natural dyeing are:
Citrus fruits (lemons, limes, oranges, grapefruits)
Vinegar (acetic acid)
lactic acid
What makes something an alkaline assist?
An alkaline substance is a substance that has a pH value above 7 on the pH scale, which means they are more basic or alkaline than a neutral solution (pH 7). These substances have a higher concentration of hydroxide ions (OH-) than hydrogen ions (H+).
In natural dyeing we traditionally use:
Baking soda (sodium bicarbonate)
Soda ash (sodium carbonate)
Ammonia (urine!)
Hydrated lime
Some minerals and rocks like the natural limestone I have brought back from Mexico.
Wood ash, is a wonderful mild alkali commonly used in traditional dye recipes and our indigo from El Salvador is extracted using wood ash.
I highly recommend checking your pH levels regularly while dyeing, so you start getting an intuitive sense of the direct connection between pH and dye color.
My second recommendation is playing around: take three samples of your dye water. One you will keep as is, to one add some soda ash and to the other add some vinegar. Just see what happens and start understanding through doing.