What we know, what we don’t know and all the stories we tell about mordants. text by Cecilia Raspanti
Mordants are the matter we use to support the further fastening of certain dye molecules into the fibers. The majority of botanical dyes seem to require a mordant in order to fasten to both protein and vegetable fibers in a stable way when using a heated dye bath process. Some dye matter does not require a mordant at all, or will offer a different shade of colour without it. Mordants also come in various forms and can be combined with fibers either before or after dyeing, or in combination with one-another.
Mandragora plant, Erbario di Trento, 1440
When we use the word “mordant” we use a word coined in medieval times, when the notions of female humane-look alike plants like Mandragora [1] was also considered (scientific) truth.
Therefore the etymological definition of the word mordant is always holding us into the medieval -mordere, so -to bite into the textile. Yet, that may not be the most accurate depiction of its function.
A mordant is instead a metallic salt, it’s a “connector” bridging between the fibers and the biochromes- by nesting itself into the fibers or around the fibers.
It is not per se “biting” into the textile – in fact when we look at the molecule of aluminium – we see how it’s ready to “bridge”, to act as a “connector”. It is in fact more likely that the biochrome (the dye molecule) that “bites” into the mordant. This also refers to a process of chelation.
Rocks, plants or crystals for brightness – the aluminium mordants
alum crystal rock from the biochromes color archive collection
Aluminium mordantsexist in a variety of forms, from “crystal rocks” to plants, all the way to purified crystalline fine powders. Its chemical composition also differs in each state, so does its application and use, or process for implementation.
This class of mordants has the power to bring out the true brightness in biochromes, sometimes revealing hidden colours, that would otherwise not show in water. When we look at dye matter through the lens of alums – we gain the ability to see bright yellows, fiery reds and sour greens.
Within our practice we mainly work with Potassium Aluminium Sulfate and Aluminium Acetate, but have experimented with A. lactate, A. sulfate, A. triformate, as well as botanical sources of aluminium such as Symplocos, during Cecilia’s knowledge exchange and workshop in Bhutan; as well as the local and protected club moss variety Lycopodium. These last two are grouped together with many other botanical sources and are called Aluminium bio hyper accumulators. You can read about some experiments with aluminium bio-hyper-accumulators in our other stories and papers.
Crystal rocks and botanical alum sources feel much more “natural” forms of matter, fostering a different relation between the dyer and the matter itself and in consequence to the process of mordanting and dyeing.
On the other hand, these materials are less pure, contain other molecules or even other metallic salts such as ferrous related ones, that can dull the colors of the final results.
Rusty nails, red soils and green powders for sadness – the ferrous mordants
Ferrous mordants are the essence to call upon the darkness present within biochromes. They have the ability to let botanical tannins surface, turning yellows into greens; reds into purples and maroons, oranges into brown and so on. When tannins are strongly present in the dye matter, the resulting biochromes may turn entirely black, or shades of black. Ferrous mordants act on the tonal value of colors, adding shade.
Their appearance and range in terms of form is as vast as the aluminiums ones. Iron presents itself in natural and man made forms, as well as a variety of purified chemical powders. One of its most present natural forms is soil, iron rich soil often has a rusty appearance, activated by the oxidation of the iron components. Similarly, rusty iron nails undergo oxidation, and are an easy, yet unstable or unquantifiable source for ferrous mordant. Also in this class of mordants, we see the use of purified powders as most consistent for dyeing.
Sidekicks, friends and partners – the role of binders, assists and tannins
Mordants are an incredibly useful matter and play an essential role in the binding of most biochromes to fibers. They also often like to work in the good company of assists and tannins, or can even be replaced with binders in certain conditions.
Binders – binders are not mordants, yet they are often presented in a similar category. They have a similar function, yet act in a different manner: they do not fasten the dye molecules into the textiles or fibers, but rather, onto the fabric: they superficially bind a dye molecule on the surface of fibers and textiles. A well known binder is soy – which enzymes bind to the surface of fibers and are able to bind themselves again with a soy based pigmented inks.
oak galls, one of the most concentrated natural forms of tannins in nature, image from the biochromes archive
Tannins – these all organic nuts, fruits, pods, barks or woods and roots are not truly mordants, yet in certain cases they can almost replace a mordant or form the necessary bond with a metallic mordant to fixate a bio chrome more stably into vegetal fibers. They are the bridge between the organic world and the inorganic, allies for color light and wash fastness. Every place in the world has its own local variety and traditional source of tannic acids, abundant and strong, often also used for writing inks when married to iron.
Assists – as the word suggests, are the assistants necessary for certain dyes to truly come to life. Often, they are sharpening the conditions of the dyes bath, bringing them back to ones that are similar to the plant’s best growing conditions. An alkaline soil loving plant often benefits from a slightly alkaline dye bath to truly bloom.
They are both organic and inorganic, can be made from waste matter or have culinary uses too; or can be entirely lab made and present themselves as inert powders.
