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Before the invention of synthetic dyes in the mid-19th century, the colour from plants was the main way to change fabric, often by employing natural dyes in the three primary colours of red, yellow and blue and combining them to great effect. Plants such as indigo and woad (for blues), red-veined sorrel and madder (for reds) and coreopsis, cota tinctoria, greenweed, yarrow, weld and feverfew (for yellows and oranges) could all dye fabric to different intensities depending on solution strength and dyeing time. All of those plants are now in the RSC test dye garden.
The colour comes from different parts of the plants, often the flower petals but also the roots and leaves, and are classified as either Grand Teint or Petit Teint depending on colour intensity and resistance to running.
The dye garden in August
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Throughout the 2023 growing season Lisa, Helen and a team of volunteers have been weeding and keeping the garden tidy and promoting natural pollinators into the space. A twice-weekly harvesting schedule has given Helen the plants she needed to create test dye conditions and record how different fabrics react to individual solutions. The dyeing process varies for each plant species.
"Some of them you have to harvest the whole plant straight away. And things like the indigo, you have to process it immediately. You can freeze it, but we haven't currently got facilities for that," says Helen. "Other plants like the coreopsis, it's basically like deadheading the flowers. And then we store those in vegetable bags, and dry them out in our hot box. Then those are stored in an airtight container so that we've eventually got enough to dye some items of costume. Then you soak them, put them in water, it's a bit like making tea."
Helen also explains the more complicated process around indigo and woad, which use oxidation and fermentation to create their rich blue colours. Although indigo powder is blue, it won't dye fabric without other scientific processes. First, the indigo needs a reducing agent such as fructose, henna powder or madder root to ensure it properly dissolves in an alkaline base, which is created using calcium hydroxide. The combination of the indigo into the alkaline turns the dye bath a yellow-green colour ready for dyeing. Finally, it's the introduction of oxygen, either when the fabric is removed from the dyeing vat or placed in a water bath, which then turns the fabric blue, as if by magic.
Helen's experiment book keeps a log of plant usage, solution strength, materials test-dyed and dyeing time to achieve different results
