All plant materials contain a mix of different phytochemicals. I am not going to re-invent the wheel and I will quote Wikipedia on the definition of this word:
Phytochemicals are chemicals of plant origin. Phytochemicals (from Greek phyto, meaning "plant") are chemicals produced by plants through primary or secondary metabolism. They generally have biological activity in the plant host and play a role in plant growth or defense against competitors, pathogens, or predators.
Part of these phytochemicals also give color, and only a part of these colors are the stable, light- and wash fast pigments we use in natural dyeing.
It is important to understand these different pigment groups, so we can anticipate if a plant material will dye, why it dyes and how stable this dye will be. In this article we discuss the first group; Flavonoids
There are over 5000 naturally occurring flavonoids that have been characterized from various plants. They are classified according to their chemical structure, and are divided into subgroups, each subgroup has their little list of flavonoids. I have put together the ones you would be looking for (or should be avoiding) that have relevance to color when dyeing.
One major group of flavonoids are Anthocyanidins and Anthocyanins
These common reds and oranges of nature are the dyestuffs we prefer to avoid. They are fugitive colorants with poor color fastness and low chemical and thermal stability. They change in appearance over time when exposed to light, temperature and humidity. We can find these pigments for example in petunia’s, red cabbage, black beans.
Specific names of these phytopigments are;
Anthoxantins are divided into Flavones and Flavonols
These pigments are generally whiter in an acid medium and yellowed in a ph neutral or alkaline medium. This is the reason we add a bit of chalk to the dye bath. (See this blog for a comparison with and without chalk) You can also use a pinch of soda ash.
Flavones and flavonols always need a mordant salt like alum to connect themselves permanently to the textile.
I only list those most important to dyers.
Quercetin (Oak, eucalyptus, onion skins, St. John's-wort)
Kaempferol (Mullein, sage, tea, onion skins)
Fisetin (persimmons, quebracho)
Rhamnazin (Rhamnus bark, Buckthorn berries)
Morin (Osage Orange, Old Fustic
This group of flavonoids is also very rich in tannins. The tannins assist in fastness of these dyes. In order to 'catch' the flavans in these dyes you must mordant the fabric with alum and the dye bath should be heated. You will see a clear difference between cutch on unmordanted and on mordanted fabric. The result on alum mordanted fabric being much more golden brown.
Gallocatechin (Cutch, Green tea)
Theaflavin (oxidation products of catechins, like fermented tea)
In further installments of this blog series I will discuss other phytochemical groups such as Naphtoquinones, Caretonoids and Anthraquinones.
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