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A Coloured Viewpoint

by India Flint
Posted on April 21st 2010

Presenting a lecture on plant dyes at a conference in Denmark back in 2000 I was quite viciously [but fortunately only verbally] attacked by the conference chair who stated unequivocally that “it was a well- known fact that boiling plants to extract dye rendered them highly toxic and thus people should stick to synthetic colours which are much safer” and then used her position to deny me my right of reply. It is this sort of misinformation that has clouded the reputation of ‘natural dyeing’ in recent times. Certainly when the traditional adjunct mordants such as chromium, tin, copper or iron salts are used in the application of dyes the resultant residue should in principle be disposed of at a toxic waste facility; although the unpleasant truth is that these have been used with [almost] gay abandon by home-based dyers, almost certainly without proper safety procedures. “A Manual of Dyeing Receipts” authored by James Napier in 1853, just a few years before William Henry Perkins accidentally stumbled on a mauve dye while attempting to synthesize quinine [but unknowingly using contaminated laboratory equipment] lists a horrifying compendium of chemical adjuncts that would indeed make a plant brew quite poisonous [irrespective of the inherent toxicity or not of the species used]. How would you feel about wearing cloth against your skin that had been processed using such substances as ‘cyanide of potassium’ or ‘protoxide of uranium’? It brings to mind the legend that Napoleon Bonaparte could have been deliberately poisoned using arsenic tainted wallpaper. Whether or not the story is true, it would certainly have been possible to poison a person using chemically contaminated clothing or furnishings; one could even speculate that the rate of infant mortality in certain cultures might well have been influenced by the way in which colour was fixed in cloth, how well that cloth was rinsed or neutralized and if toxic substances may have leached out in the presence of human bodily fluids. But I digress.

Fairly early in my chosen research path it dawned on me that in many cases where such adjuncts were used, the plant brew was acting as an acidic mordant and the colour was actually being derived from the metallic salt. Consider the case of Potassium bichromate, a popular [and horribly carcinogenic] mordant in the making of yellow dyes. Reading the many dye recipes that recommend this substance as an assistant it becomes apparent that there is more than a coincidental relationship between the paint colour ‘chromium yellow’ and yellow dyes where chromium salts have been employed as the ‘assist’.

Reading about the chemical make-up of that the much underrated genus eucalyptus [still my favourite dye source] I was astounded to discover that species of this plant contain within the leaves everything necessary to fix substantive colour on protein fibres and that applying mordants to cloth in advance of dyeing was not actually necessary [unless possibly as a colour modifier]. The most important adjunct in a eucalyptus dyebath is in fact the water used as the substrate. Eucalyptus dyes are extremely sensitive to variations in pH as well as to dissolved salts and perform at their very best in neutral to slightly acidic water. Heavily contaminated waters [such as those loaded with iron or copper salts] may however be used to advantage as a pre-mordant in order to influence the shade to be achieved from the dyebath. Soaking wool or silk fabrics in such solutions [for example bore water or seawater, or simply rusty water from an old tin can], then allowing them to dry before processing in an optimally prepared eucalyptus bath offers exciting possibilities indeed.

The almost accidental discovery that eucalyptus leaves could be used for printing came about through the keeping of hens. They’d made their nest using old dried eucalyptus leaves, dutifully laid their eggs and then brooded quietly while I lazed indoors on a few wet days [venturing out only to sling kitchen scraps into their run]. When I finally discovered the eggs, they had taken up the print of the leaves on the surface. I thought a little about the way in which we dye our Easter eggs each year and mused that [given onion skins would also print cloth] something similar might be achieved using eucalyptus. The gentle reader will be able to appreciate my utter astonishment when a blue-grey leaf printed a rich deep red. Further thought led me to the conclusion that as this print occurred in the middle of a cloth bundle to which only steam had penetrated, the resulting colour was likely to be the outcome had the eucalyptus leaves been processed in pure water. I was right, but only partially and must now admit that the theories published in my Masters thesis, were incomplete…although on the right track. . The eucalyptus is an astonishing genus and the more I work with it, the more I find there is to learn. I now know that the first ecoprints from a eucalyptus leaf will give one a very good idea if the colour to be had from the first boiling but that the second print can be quite a different colour, such as lime green [after an initial orange or red]. I have also found that when the leaves have been boiled for 45 minutes or so [to extract the brightest dye] they can still be used for printing, again with often surprising results.

Eucalypts also behave differently at different temperatures – the colour extracted not only depends on the heat available at the time of extraction but also on the heat [or lack of] during application to the cloth. For example if a dyebath were allowed to cool overnight before immersing the cloth to be dyed, the resultant colour will not be as bright as if the cloth had been dropped into the hot, fresh dye. These possibilities combined with the fact that every part of a eucalyptus gives some sort of colour, that fallen dry leaves yield different results to fresh picked [as well as sometimes dramatic differences in dyes from leaves depending on which part of the tree they were sourced from] and that the intensity of each season has an influence would indicate that a dyer could quite contentedly spend the rest of his or her life simply working with one tree.

The eucalypts are unique in that the dyes they produce contrast so dramatically with the fresh foliage but they are not the only plants that will print on to cloth. Most plant species will make a mark on protein fibres provided they are bundled firmly enough and given time and the appropriate conditions and the wonderful thing is that those noxious mordants so liberally used in the past are not necessary at all. So my perhaps Danish colleague might like to review her opinion of plant dyes…