This post is all about the differences and commonalities between natural dyes vs. synthetic acid dyes. But first, let’s start with a general definition:
What is a Dye?
A dye is a colored substance that chemically bonds to a substrate. This distinguishes dyes from pigments which do not chemically bind to the material they color. The dye is generally applied in an aqueous solution. It may require a mordant to improve the fastness of the dye on the fiber.
Textile dyeing dates back to the Neolithic period. Throughout history, people have dyed their textiles using common, locally available materials. Before 1856, only natural dyes were available.
As it is often the case in science, the discovery of synthetic dyes was a serendipity. William Henry Perkin, an eighteen-year-old English chemist, was searching for a cure for malaria. Accidentally he discovered the first synthetic dye. He found that the oxidation of aniline could color silk.
Dyes are classified according to their solubility and chemical properties. Nowadays, there are lots of different types of synthetic dyes available. But since acid dyes are most common for dyeing yarn, this is what this post will focus on.
What are Natural Dyes?
Natural dyes are dyes or colorants derived from plants, invertebrates, or minerals. The majority of natural dyes are vegetable dyes from plant sources—roots, berries, bark, leaves, and wood—and other biological sources such as fungi.
What are Acid Dyes?
Acid (anionic) dyes are water-soluble dyes applied to wool and numerous other natural and synthetic fibers. Acids can damage certain fibers, such as cellulose, which require different kinds of dye. The dyes in this class vary in their chemical composition but all use an acid bath. These dyes produce bright colors and have a complete color range with varying colorfastness.
What are Vat Dyes?
The name vat dyes refers to the method with which dyes of this class are applied. Vat dyeing is a process that refers to dyeing that takes place in a bucket or vat. The original vat dye is indigo, formerly obtained only from plants but now often produced synthetically. Vat dyeing differs significantly both from the standard natural dyeing process and the use of acid dyes. I will cover the process of vat dyeing in more detail in a future blog post.
Commonalities of Natural Dyes vs. Synthetic Acid Dyes
Now that we’ve covered the basic definitions, let’s have a closer look at the procedures of dyeing yarn with natural dyes vs. synthetic acid dyes. On the surface, the processes are rather similar.
You have to
- prep and scour (wet) the yarn
- put it in a pot filled with water and dye
- heat it and let it simmer, then let it cool off
- wash off any excess dye and
- hang it up to dry.
The differences are in the details, though.
Differences of Natural Dyes vs. Synthetic Acid Dyes
Preparation of the Dye
Synthetic dyes are ready for use and don’t require any prep work.
Preprocessing of natural dyes is often necessary, depending on the specific dye material. Usually, you need to heat the dyestuff in advance in order to create a saturated dye bath. Some of them require pouring boiling water over them and letting them sit overnight. Barks, for example, have to be soaked in water for several days or even weeks before the color can be extracted by heating them.
Natural Dyes often require a mordant to ensure sufficient colorfastness. A mordant or dye fixative is a substance which is used to set dyes on fibers. Mordanting is usually an additional step in the dyeing process which is done before the actual dyeing itself.
Synthetic acid dyes, on the other hand, don’t need a mordant to bind to the yarn. They do, however, require an acidic environment. This is usually created by the addition of citric acid or acetic acid (vinegar) to the dye bath.
Natural dyeing, on the other hand, can be performed in various pH environments, depending on the dye material.
Duration of the Dyeing Process
Synthetic acid dyes generally bond to the fibers pretty well and only require a short amount of heating.
With natural dyes, this process can take a lot longer. It is often advisable to let the yarn cool off and sit in the dye solution overnight to allow for more dye uptake.
Dyeing yarn with natural dyes is a lot more water intensive than using synthetic acid dyes. Since synthetic acid dyes create a bond with the yarn very well, there is not a lot of excess dye left in the dyebath. Washing and cleaning the yarn afterwards before hanging it up to dry is therefore a smooth process.
With natural dyes, however, there is usually quite a lot of color left in the dyebath. And more excess dye is going to rinse out during the washing process. The yarn has to be washed out thoroughly until the water runs clear. This will avoid any excess dye to come out when washing the knitted piece. Just be aware that washing the yarn can take it’s time when using natural dyes.
Due to their natural origin, batches of natural dyes are never exactly alike in hue and intensity. In fact, the color results of many dye materials also vary throughout the seasons. In addition, the location where the dyestuff grew also plays an important role.
The manufacturing of synthetic acid dyes, on the other hand, is done consistently by using the same recipe and conditions. Therefore the batches will be much more similar to each other.
And there you have it, a comparison between natural dyes vs. synthetic acid dyes. You might argue that the use of natural dye material is more sustainable. But you also have to take the higher demand of water and electricity of the natural dyeing process into consideration. As it is so often the case in life, it just isn’t a black and white situation. There are benefits and disadvantages to both forms of dyes.
Further Reading Recommendations:
If you are interested in learning more about natural dyeing, I have written several posts highlighting different aspects of natural dyeing. These are just two examples, you can find all the posts in the natural dyeing category of the blog:
If you want to learn more about dyeing yarn with synthetic acid dyes, I can recommend this series of Nicole from Hue Loco. She made several about how to dye tonal, variegated and speckled yarns and a checklist to help you get started:
Pin It For Later: Natural Dyes vs. Synthetic Acid Dyes
Booth, Gerald (2000). “Dyes, General Survey”. Ullmann’s Encyclopedia of Industrial Chemistry. Wiley-VCH. doi:10.1002/14356007.a09_073. ISBN 3527306730.