Fugitive Colourants vs True Natural Dyes
Is your colourant source (flowers, leaves, fruit, seeds, etc.) black, blue, purple, red or pink? Those visible colours are generally from anthocyanins, a class of naturally occurring chemicals known for their instability. They are easily degraded by ph, temperature, light, oxygen, metal ions, and many other factors and, therefore, are never reliable dye sources for textiles or visual art materials. They are not lightfast or washfast, and neither fibres nor mordants can not bond to them. Anthocyanins are commonly used in culinary applications, as they tend to be soluble in lipids (fats and oils) and don’t need to last long.
Another type of fugitive coloured compound found in plants is chlorophyll, which gives us the Plant Kingdom’s glorious greens. Like anthocyanins, it can not form stable molecular bonds with fibres or mordants.
How To identify Anthocyanins…
Anthocyanins are influenced by pH in predictable ways - tending to red with lower pH and to green with higher pH.
This image explains how to tell if a colourant is fugitive, to save yourself any heartache. So if, for example, you use a purple flower, a blue seed, or a red leaf, and you can shift it to blue, green or yellow with increasing alkalinity, then you are dealing with a completely unstable, fugitive colourant.
A general guide is that a reliable natural dye stays broadly within the same colour family as pH is shifted (for example, it may shift from red to orange), whereas a fugitive colourant changes to a completely different colour as pH is shifted (for example, it may leap from blue to red).
To help new natural dyers get off to the best possible start…
There is an enormous amount of misinformation on the internet about natural dye sources. Defer, instead, to the historical record (https://www.mamiesschoolhouse.com/blogarchive/2021/7/17/how-do-we-know-its-a-dye-species-historic-record), and to knowledgeable contemporary dyers.
Black, blue, purple, red, or pink natural dyes are generally…
hidden, such as red dyes hidden inside the roots of members of the Rubia genus (madder), or inside the bodies of various insects, such as cochineal, kermes, and lac;
in the case of blue, hidden as a water insoluble pigment inside indigo and woad leaves;
or they are made from combination dyeing (i.e. over-dyeing one primary colour with another primary colour).
It’s OK to play with fugitive colours, many can be very pretty and fun craft projects with children, for example, but children also deserve facts. I have also seen some artists intentionally use fugitive colourants in exhibits exploring themes of impermanence, where they are the perfect choice.
If you are selling items coloured with fugitive sources, it is dishonest to not disclose to your purchaser that the colour will quickly disappear, and it contributes to a still widespread misunderstanding that natural dyes are not reliable. In such instances, it is the seller - rather than the world of proper natural dyeing techniques - that is unreliable.
There are people for whom natural dyeing is a casual hobby, and people for whom it is a serious craft and business, steeped in learning the rich history, chemistry, and artistry. Both are ok.
As a natural dye educator, I prioritize accuracy and a respect for the rich, reliable traditions of which we are now the custodians, and endeavour to ensure that those starting out in this craft can start from a foundation of historic evidence and scientific fact.
Chemically Identifying Reliable Natural Dyes…
The chemistry of reliable natural dyes is expansive, but generally involves the chemical categories described in this brief video.