Exploration in coffee and indigo over-dyeing
Indigo can impart some pretty stunning shades on cloth but after working with it for over a year it can feel a little tiring having to look at blue stuff all day. So a few weeks ago we started throwing another dyestuff into the mix: coffee! With its palette ranging from light creamy beige all the way to coal black it yields a great assortment of colours that pair well with indigo, slightly reminiscent of the indigo-kakishibu (fermented astringent persimmon) combination found in Japan.
In our previous work we physically rubbed the coffee grounds into the fabric (which incidentally promotes circulation in your palms and makes them super soft) to give a faded toned-down look to otherwise stark blues and whites. By rubbing we created a mechanical bond between the coffee pigment and the cloth, somewhat akin to how indigo pigment behaves by becoming trapped in weak electrostatic bonds within the fibres. Most natural dyes however do not work like this and require the cloth to be pretreated with a metallic salt which allows the dye to “bite” into the fibre once it is submerged in the dye solution. By applying various concentrations of thickened mordants (alum and ferrous sulphate) directly onto the cloth with a brush and then submerging it into a dye bath of coffee we were able to achieve more colours than by rubbing alone. The mordanting process also gives fastness and (relative) permanence to the colours.
The shades from the initial test pieces (#1,#2 and #3 from the left) were too light so we also began treating the fabric with tannic acid prior to mordanting and dyeing which intensified the colours. For #4 and #5 the tannic acid was extracted by simmering pomegranate skins (#4 had various mordant concentrations brushed on the flat fabric and #5 was stitched and compressed prior to the mordant application. Both pieces were then dyed in coffee). The pomegranate left an orange tint which we did not want for our final project so for test piece #6 we extracted tannin from myrobalan which gave us the colours we wanted. We then stitched, compressed and manipulated various fabrics before treating them. The following works are a four-step process: treatment with tannic acid extracted from myrobalan, application of ferrous sulphate/alum mordant, dyeing by simmering in coffee extract and a final over-dye of indigo (except the first piece which omits the indigo over-dye).
We especially liked the last piece and decided to reproduce it on a bigger scale. This pattern is most likely going to be something that we will incorporate into our future project.
These new colours are unexplored territory for us and the process of discovering how the myriad of variables can be tweaked is irresistibly exciting. It seems there are so many things that can be taken into account when working with natural dyes. Do you boil or simmer the dye material during extraction? For how long? What is the pot made of? Does the water have a neutral PH or any contaminants in it? Which metallic salt will you use as a mordant? At what concentration/combination ratio? Does the fabric receive the mordant before, during or after the dyeing? Are your hands free of contaminants that upon contact with the cloth may result in uneven dye penetration? Are there variations in the pigment based on which month of the year the plant material was collected or whether the harvest came from the North or South side of the trunk (as is the case for certain species of eucalyptus)? The smallest seemingly insignificant details can all affect the outcome and perhaps that’s one of the reasons why we are having such fun with natural dyeing: because the process itself feels like playful interaction with another entity that is very much alive, with its own mysteries, nuances and rules that we can learn with time, experience and luck to bend but never break.
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