MADDER ROOT, RED DYE, RUBIA TINCTORUM
Madder root is a traditional dye plant and one of the oldest natural dye colours in the world.Scouring pieces of madder root rootstock in near boiling water yields the dye Alizarin. On pre-stained yarn, the dye is transformed into a varnish, resulting in a delicate, earthy or fiery and powerful red – depending on the amount of madder root used. This is why Romans named madder root “Rubbia”, which is the generic name still used today.
RESEDA or WELD, RESEDA LUTEOLA
Reseda is the most frequently used plant for producing yellow dye.The plant is easy to cultivate as it grows like weed. In contrast to madder root, the dye is only found in the part of the plant that grows above ground. The dye luteolin is derived by boiling the dried plant; depending on the amount of Reseda applied to stained yarn, the nuances of yellow range from lemony to golden.
In addition to madder root and Reseda, Indigo is one of the oldest known plant-based dyes. Indigo plants contain a water-soluble and colourless glycoside, called indican. When immersed in water and then exposed to warming sunlight, the plant particles fully decompose in an anaerobic fermentation process. During this process, indican releases indoxyl and glucose, thereby turning into a yellowish solution. Upon stirring the viscous pulp, it combines with oxygen and becomes blue. The dye obtained in this way is insoluble in water and settles at the bottom of the container.
Dried and then ground into a fine powder, the colour is ready for dyeing. In a further step, indigo is again transformed into a water-soluble form (vatting) for the dyeing process. During this process, the dye changes its colour from violet-blue to yellow. After the fibre has absorbed the dye, adding oxygen reverses the vatting process. The dye again becomes insoluble in water, remaining in the fibre and maintaining its blue colour.
COCHINEAL, OPUNTIA COCHENILLIFERA, COCCUS CACTI
The cochineal is an insect that lives on Opuntia cacti; its glands produce carmine. The dye was already highly valued during the time of the Aztec empire. It is produced by immersing the dried insects into hot water, subsequently yielding a range of light to dark red on the stained yarn, depending on the amount of carmine used.
Logwood, or bloodwood, is the most important dyeing wood. The heartwood of the Campeche tree, which grows in South America, is the main source of haematoxylin used as a dark purple and black dye colour. In 18th-century Europe, this constituted the first dye with which people were able to produce these colours with sufficient colour fastness.Prior to the discovery of synthetic dyes, this resource had a huge economic significance. Today, the dye is still widely used for medical purposes.
MORDANTS (ALUM, TARTAR, IRON, SODA)
In order to improve the colour-fastness or to influence colour nuances of pre- or post-stain yarns, ferrous sulphate, alum, potassium aluminium sulphate and tartar are used as dye-fixates.