Natural dyes produce wonderful colors and that’s all due to chemistry! That’s right, science baby!
But do you know why so many flowers give yellow? Or why avocado skins will produce a pale pink?
The answer is in the compounds of the dye plants, the phytochemicals. Let’s talk natural dyes and chemistry today and break the science behind these dye plants compounds!
The basics of natural dye chemistry:
I think it’s easier to start by classifying the dyes by colour. So, let’s divide them into groups of colors.
Yellow:
Yellow is the most common color to obtain with natural dyeing. It outnumbers the other groups of colors and most of them contains the flavonoid compound. Don’t worry, we are going to go further into the details of natural dye chemistry about that one.
Among the most well-known plants giving yellow, we can mention weld (Reseda luteola), marigold (Calendula Officinalis), chamomile (Matricaria chamomilla), pomegranate (Punica granatum) and turmeric (Curcuma longa).
Blue:
Blue is one of the rarest colors in nature. Two of the most well-known plants to give blue are indigo and woad.
The Indigofera tinctoria is native to India while woad (Isatis tinctoria) is native to Central Asia and has been widely cultivated through Europe. Both contain indigotin. We are going to talk about it again later in the natural dyeing chemistry section of the indigoid.
But to finish with the plants giving blue, we can also mention two other sources of blue: wild Guava (Careya Arborea, a tree species native to India, Afghanistan and Southeast Asia) and Tsuykusa flowers (Commelina Communis, native to East Asia and the north of Southeast Asia).
Red:
Red dyes (and I include pink as well in this group) are mostly found in roots, bark and some insects.
A true red is difficult to obtain but like often with dyeing, it’s all a matter of experimentation and hard work.
The most well-known dyes producing red can also give you ranges of orange and pink, mainly madder (Rubia tinctorum), cochineal (Nopalea cochenillifera) and lac (Kerria lacca).
Green:
Green dyes are also very rare. That’s definitely odd since the colour coming to mind when talking about nature is green but that’s natural dyeing chemistry for you!
It’s more common to obtain green dyes by overdyeing yellow fabric or yarn with indigo or using a modifier like nettles + copper. Though depending on the time of the year, the soil, etc, some dyers will get a lovely pale green with only nettles.
Orange:
Orange dyes can be found in the plants giving red and yellow dyes.
I really love madder to get vivid orange but you can get a whole range of color from pale pink and peach to several shades of orange all the way to the precious red.
Orange comes from the caronotoid compound, which we will explore further in one of our natural dyeing chemistry sections below.
Apart from madder, you can also get orange with dahlias and annato (Bixa Orellana).
Brown:
Let’s finish this list with brown dyes. They mostly belong to the alpha naphthoquinones compound group.
If your eyes are starting to glaze over, don’t worry we are covering this one as well.
For now, let’s keep in mind that you can get brown easily with walnut husks and henna.
Main natural dye chemistry groups:
When I first started with natural dyeing, I stumbled across terms like flavonoids and indigoid. It was only when I bought my first books about natural dyeing that I found some explanations.
That’s why I thought it would be nice to break down natural dye and chemistry into small easy chunks together here.
Natural dye chemistry: the first group
The Flavonoids:
Let’s start with the most common group in natural dyes.
Like I mentioned above, yellow dye is the easiest and most common dye you can get with natural dyeing. Most of these yellow natural dyes come from flavones and isoflavones, the subgroups of flavonoids.
The World Health Organisation have encouraged the use of flavonoids again in recent years for textile dyeing but also cosmetics and pharmaceutical products since it’s non-toxic and sustainable.
I already mentioned examples earlier but let’s not forget about onions skins and the luteolin dye, the oldest European dye for yellow.
Natural dye chemistry: the second group :
The Carotenoid:
Carotenoid of course calls to mind carrots since they are the main source of carotene. Yeah, orange!
If we want to go a bit deeper into the science here, the orange color is due to double bound conjugation.
A popular but expensive source of orange in the kitchen would be saffron.
Natural dye chemistry : the third group :
The Indigoid:
Indigo is a vast subject that we will explore in further details in future blog posts (I’m really excited about this research!) but for now, let’s tackle the indigoid.
The higher percentage of indigotin in the indigo you will use, the deepest and darkest blue you will get.
The seed of the Indigofera Tinctoria is the part that contains the dye. It’s a whole chemical process since the plant needs to be fermented with microbial communities. These bacteria occur naturally and are indigo-reducing bacteria. The fermentation process leading to indigo reduction can take up to two weeks. The glucoside is then completed, the extract converts from indoxyl to indogotin and tadaa we get our indigo.
Note that I simplified the explanations a lot and I’m no scientist so make sure to check the sources I’m linking to below if you want to go more in depth in the chemistry of indigo.
Natural dye chemistry the fourth group:
The Anthraquinone:
Anthraquinone are a chemical compound to get red dyes from plant and insects. These dyes have great lightfastness.
The most popular dyes with the anthraquinone compound are madder, cochineal and lac.
Natural dye chemistry the fifth group:
The Alpha naphthoquinones:
The alpha naphthoquinones compound is found in popular and easy to obtain dyes like walnut tree (bark and husks) and henna.
The use of henna on cotton fabric has shown strong protection again UV thanks to the alpha naphthoquinones chemical compound. This shows once again the importance of natural dyes for sustainability and our future.
Natural dye chemistry the sixth group:
The Dihydropyrans:
The dihydropyrans compound are related in chemical structure to the flavones.
The most popular dyes containing dihydropyrans are logwood and brazilwood.
Logwood chips (Haematoxylum campechianum) give beautiful shades of purple while brazilwood (Caesalpinia) offers a vast range of pink to deep reds.
Brazilwood refers to two species of trees:
Caesalpinia echinata from Brazil, an endangered species of trees and listed as protected by the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES).
The second species is Caesalpinia sappan from Asia (which you can find sometimes referreed as sappanwood). Caesalpinia sappan isn’t an endangered species and is the one you should use for natural dyeing with brazilwood.
So, it’s really important to be careful and check the source of your brazilwood.
Natural dye chemistry: the seventh group:
The Anthocyanidins:
The most popular dye containing anthocyanidins is the carajurin (from the leaves of Bignonia chica), giving orange.
The anthocyanidins are found in red, blue and purple flowers and fruits and are water soluble pigments from the phenolic family.
Natural dye chemistry : the eighth group
The tannins:
Tannins are also compounds from the phenolic family.Tannins are easy to obtain since you can get them in barks, leaves, roots, galls.
They are useful to help mordant your fibers and can also give you colors with a modifier. You can use nutgalls to mordant vegetal fibers like cotton or linen and with the help of a modifier like iron, you will obtain gray.
Researches about tannins have shown its use against microbes and UV rays but also an improvement of antioxidant properties on dyed wool.
I hope you enjoyed these explanations about natural dyes and chemistry!
I think that for dyers, knitters and users or admirers of naturally dyed fabric, it’s important to understand the process behind the pretty colors.
Natural dyes have been used for millennia, not only because we, as humans, love pretty things but also for their properties like resistance to bacterias, fungus, moths and UV rays.
It’s obvious that if we want a more sustainable world, we need to pay more attention to natural dyeing, while being attentive to protected species.
If you want to dig deeper into the nitty gritty of natural dyes and chemistry, I’ve listed sources below.
And if after reading about the chemistry of natural dyeing, you want to try making science, we have a great post with 5 natural dyeing recipes for beginners.
Sources:
- Virendra Kumar Gupta (December 22nd 2019). Fundamentals of Natural Dyes and Its Application on Textile Substrates, Chemistry and Technology of Natural and Synthetic Dyes and Pigments, Ashis Kumar Samanta, Nasser S. Awwad and Hamed Majdooa Algarni, IntechOpen, DOI: 10.5772/intechopen.89964.
- Padma S. Vankar. Chemistry of Natural dyes, Resonance October 2000.
- Deepti Pargai, Shahnaz Jahan and Manisha Gahlot (January 11th 2020). Functional Properties of Natural Dyed Textiles, Chemistry and Technology of Natural and Synthetic Dyes and Pigments, Ashis Kumar Samanta, Nasser S. Awwad and Hamed Majdooa Algarni, IntechOpen, DOI: 10.5772/intechopen.88933.
Thank you for reading!
