Bringing out the colour

Bringing out the colour

24 February 2021 Robert Wróblewski 1711 views

Research into plant dyes has been conducted at the Goetheanum since the painting of the ceiling in the First Goetheanum. In 2015, Robert Wróblewski re-established the plant dye laboratory. He is studying the effect of metal fertilizing on the vibrancy and lightfastness of dyes and has reconstructed the process for producing Maya blue.

When I compare pictures painted with plant dyes and those painted in acrylic, I experience the former as more vibrant: they have something refreshing and vitalizing, conveying greater width and depth. This is why they are so highly appreciated by both artists and art therapists. However, most plant dyes have lower natural lightfastness.

Metal fertilizers

The plant dye laboratory at the Goetheanum is therefore examining how lightfastness can be increased and the range of dyes extended. The first pigments have now been produced, not by changing the laboratory process but by ‘fertilizing’ the dye plants with metals.

Take dyer’s madder, for instance, or ‘rubia tinctorum’ in Latin: this is a traditional dye plant where the red colour is contained in the roots. Depending on the manufacturing process, paints made from madder can have various hues of red.

I used copper and iron to fertilize the madder plants. The first experiments, carried out in 2016, revealed that these fertilized plants germinate later and that, depending on the fertilizer, the forms of their roots change. Most importantly, they produce different hues of red:

– When the madder is fertilized with copper, the red appears warmer, with a slightly brownish tone;

– The red from iron-fertilized madder appears colder.

Including the unfertilized plants, I now have three kinds of madder pigments. Both metal ones have very good lightfastness. The colour intensity when painted was best with the iron sample.

Based on indigo

Knowledge of how to produce the particularly bright Maya blue faded away during the 18th and 19th century. In 1931, the archaeologist Raymond Edwin Merwin rediscovered the recipe when studying wall paintings in the ancient Mayan city of Chichén Itzá, in the Mexican state of Yucatán. The Mayas used it also for ceramics and books. How can the process be reconstructed from historical indications?

Maya blue is derived from indigo. Natural indigo can be obtained from various plants. In Asia (Caucasus) and Europe it used to be made from dyer’s woad (Isatis tinctoria), in Asia (India), Africa and America from true indigo (Indigofera tinctoria).

Unlike other plant extracts, indigo is not oil- or water-soluble and can therefore be used directly as pigment. But because it appears in the plant in the colourless enol form (indoxyl glucoside), fermentation and air oxidation are required to bring out the colour. The indigo derived from Indigofera tinctoria is always black-blue, while purer, brighter hues of blue result when it is mixed with palygorskite and then heated. No special lab equipment is required for this process, nor does it involve any toxic substances and material costs are low. The process can easily be used by artists or in chemistry lessons in Waldorf schools.

Producing Maya blue

Compared to the duller dark blue of indigo, Maya blue is a bright turquoise blue pigment that is also remarkably light-resistant. It widens the otherwise rather limited palette of blues in plant dyeing.

Maya blue can be manufactured in three ways:

– by combining indigo with a mineral and heating the mixture to at least 100 degrees Celsius;

– by making the indigo powder water-soluble using alkali and a reducing agent and mixing the hydrated indigo – a yellow to yellowy-green fluid – with the clay mineral palygorskite;

– by mixing indigo or woad leaves with palygorskite and water and then processing them further using an alkali and a reducing agent.

The colour obtained from woad is slightly brighter than that obtained from the indigo plant, partly due to the much lower indigo content. Woad and the Mexican indigo plant produce a more greenish hue, while the pigment of the indigo plants from India is a warmer shade.

If the pigment is mixed with palygorskite alone, the colour will be less resistant than when using the second method. But the method is still fine to use in school teaching or in art therapy. If mixed with copal, the colour will be more resistant to light. The second method results in a turquoise that is comparable to the one used in Mayan artefacts. The pigment is even more light-resistant.

The next step will be to follow Rudolf Steiner’s indication on influencing crystallization in the manufacturing process with poisonous plants. Again, I will test for lightfastness in particular. If the results are convincing, more plants will be available for the production of plant dyes.

The plant dye laboratory belongs to the Visual Art Section and is supervised by Torsten Arncken from the Natural Science Section.