True Hues

Brinda Gill talks to Dr. Bosco Henriques, a doctorate in plant molecular biology and founder of BioDye India Pvt. Ltd., one of India’s foremost 100% natural dyeing units, about his thoughts on the attributes and potential of natural dyes.

- Brinda Gill

HOW ARE DYES BROADLY DIVIDED AND WHAT ARE THEIR KEY ATTRIBUTES?

Dyes are broadly divided into natural and synthetic. Dyes on textiles need to be tough, resistant to light, washing, rubbing and perspiration. Synthetic dyes are therefore designed by chemists to be recalcitrant. While this is good for fastness, it prevents them from degradeding in effluent treatment plants. Natural dyes need a mordant to colour textiles (indigo is an exception). The dye-mordant complex bestows the coloured textile with its fastness property. The natural dyes and tannin mordants are biodegradable.

Synthetic dyes exhibit very little batch-to-batch variation, and have defined and reproducible light absorption spectra. This makes blending of different coloured dyes of the same chemical class straightforward. Colour matching and reproducibility is easy with synthetic dyes.

Natural dyes, on the other hand, are a mixture of colourants whose composition varies from harvest to harvest. The nature of the colourant also changes during post-harvest storage, during extraction and post-extraction storage, for e.g., the living plant tissue of Indian madder contains the red colourant called galiosin. The sugar molecules are progressively cleaved after harvest to generate an intermediate red colorant-pseudo purpurin, which slowly decays into the third red colourant purpurin. To complicate matters further, Indian madder has another yellowish red colorant munjisthin which has inferior dye properties.