Red is a fascinating color. In the plant world there are several different phytopigments that are responsible for reds, purples and oranges. In the first part of these series we met the very unstable class of flavonoids that is present in most red flowers such as the red in poppies or the purple in red cabbage.
Anthocyanidins and Anthocyanins will fade in light to a very unimpressive gray, they often change to muddy yellows when boiled and they change color rapidly with ph changes. The only thing we should be doing with these unstable reds is a fun experiment with children, or food. Please never ever sell fibers dyes with black beans or red cabbage, the results give natural dyers a bad name.
For true, lasting reds we have to count on; Anthraquinones, the phytopigments that are responsible for a wide range of shades from oranges to reds, purples and pinks. They are not in flowers or things we easily see from the outside. They are mostly hidden in roots and barks.
Besides being an amazing dye component, anthraquinones are known as laxatives in natural medicine. Rhubarb root for example contains Physicion, which gives a red under alkaline circumstances but is also the stuff that will make you purge when you drink a tea from it.
Alkaline or acid? Most anthraquinone plant based dyes prefer a slightly alkaline circumstance, where the insect based anthraquinones give brighter red under acidic circumstances. Example; Cochineal will can change dramatically from orange-yellow below pH 4, wine red from pH 4 to 6.5, and purple-red above pH 6.5. Madder is giving its' brightest reds with a Ph of 9.
Another pointer I wish to give you regarding dyeing with anthraquinone rich plant parts is that almost all of them will give better reds when you do not use a full boil. Even a simmer can be a bit much. No dye plant consists only of one group of phytopigments. For example madder roots do not only have alizarin but also flavonoids and naphtaquinods, and the higher temperatures will bring out those pigments and 'muddy' the red.
Do anthraquinone dyes need a mordant? Anthraquinone dyes are substantive on wool and silk, but a higher wash- and light fastness is achieved by using a mordant. For cellulose fibers a mordant is always required. See also this article about substantive dyes.
Alizarin (Rubia tinctorum, ladies bedstraw roots, dyer’s woodruff)
Probably the best known and most famous anthraquinone. The concentration of alizarin in madder roots varies from 6.7 mg/g to 8.7 mg/g depending on the age of the roots, the older the root, the more alizarin it contains. For madder extracts a dye bath is made and fermented to hydrolyze the. anthraquinones from the glycosides (the sugar bond in the roots) and then filtered, evaporated and ground. Other methods use methanol for the extraction process. The alizarin concentration in madder extract varies from supplier to supplier and often per batch.
You can find an amazing video about madder lake extraction here.
Other anthraquinones that are relevant for dyers are;
Physcion (rhubarb roots, Buckthorn bark)
Rhein (Cassia, rhubarb roots)
Munjistin (Rubia Cordifolia)
Purpurin (Rubia Cordifolia)
Parietin (Curled dock, Buckthorn spec bark)
From this list we can learn that for example Buckthorn bark contains at least three types of anthraquinone. The dye component is most often from the roots or the bark as opposed to flavonoids that are extracted mostly from leaves, whole plant tops and heartwood. There are also a few sources of anthraquinones I think can be very interesting for the home dyer, such as dandelion root but this requires further research.
These are anthraquinoids from fungi and lichen. Most of these reds can be extracted with alkaline (ammoniac) fermentation.
Plant based and animal based. Anthraquinones are not just in plants, but also in insects;
Carminic acid (Cochineal)
Kermesic acid (Kermes vermilio)
Laccainic acids (lac dye)
These are all extremely light- and wash fast dyes, and were extensively used in traditional dye works of the 17th and 18th century.
In this PDF I have collected the recipes and methods to obtain the most perfect reds.
Articles used for reference and research;
Anthraquinone profile, antioxidant and antimicrobial properties of bark extracts of Rhamnus catharticus and R. orbiculatus
Anthraquinones As Pharmacological Tools and Drugs
Dyes from Lichens and Mushrooms In book: Handbook of Natural Colorants (pp.183 - 200) Authors: Riikka Räisänen