Guest blog by: Sophie Mogg
With the latest installment looking at the cotton industry, I thought that it might be interesting to follow up with a few snippets about natural dyes derived from plants. In today’s blog post I will be taking a closer look at turmeric (Curcuma longa), true indigo (Indigo tinctoria) and madder root or dyer’s madder (Rubia tinctorum).
Turmeric belongs to the Zingiberaceae family which also includes cardammon and ginger. It is a herbaceous perennial that produces underground modified stems known as rhizomes which acts as a store for starch, proteins and other valuable nutrients. Rhizomes are useful in other ways as new plants can be propagated from the rhizomes that are harvested each year. The rhizomes themselves would be boiled for up to 45 minutes before being dried in a hot oven and ground to form a powder which can be used as a beautiful yellow dye. Unfortunately turmeric is not colour-fast and so was often over-coloured with mustard or various pickles to help compensate for this. Medicinally turmeric has reported uses in Ayurvedic practices for treating colds and infections as well as the Siddha medicinal practice where it is used as an energy centre due to representing the solar plexus chakra. Several studies have shown that turmeric also has antibacterial and antifungal properties with studies suggesting that turmeric could be used as a preservative in the food industry. Turmeric is also used in cooking for savoury dishes as well as the predecessor of litmus paper to test pH.
The native location of Indigo tinctoria is unknown as it has been cultivated for centuries across Asia and Africa. Indigo is a shrub reaching approximately 2M tall that produces flowers in various shades of pink and violet. Depending upon the climate Indigo is grown in it can be an annual, biannual or perennial. The deep blue dye that is produced from this species is obtained through soaking and fermenting the leaves which allows conversion of glycoside idican into indigotin (the blue dye). The dye has also been used within paintings dating back to the Middle ages. Indigo tinctoria is part of the bean family (Fabaceae) and so is also used within crop rotation by farmers in order to improve soil quality for subsequent crops.
The madder root produces various different coloured dyes ranging from reds, to pinks and oranges depending upon the conditions the plant was grown in and how the roots were subsequently treated. It belongs to the family of Rubiaceae, the same family as coffee and is a relatively tall perennial plant with evergreen leaves reaching heights of 1.5M. The dye is extracted through the process of fermenting, drying or using various acids to treat the roots, that are commonly harvested during the first year of a plants growth. One of the more commonly known dyes is referred to as madders lake, a dark red produced by purpurin being mixed with alkaline solutions. These dyes can be used to colour leather, wool, cotton and silk but are typically used with a fixative or mordant such as alum to help the dye fix to the material.
Tea can also be used as a dye, with different varieties of tea producing their own unique shades. With any kind of dye the colour will fade with time but it can be stabilised by using vinegar. As previously mentioned in my other posts both saffron and henna are used as dyes also.
Have your say in which species appear in future installments of the travelling botanist. Our journey will soon take us to South-East Asia where we explore some more intriguing plants.
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