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Browsing by Subject "luonnonindigo"

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  • Niinimäki, Niina (2020)
    Indigo is one of humanity’s most important sources of blue color. Synthetic indigo is produced from oil refining by-products and uses chemicals that are harmful to the environment. Natural indigo would be more environmentally friendly, but it does not guarantee an environmentally friendly dyeing process, since sodium dithionite, which is environmentally harmful, is often used to reduce indigo. This study examines the dyeing of cotton with woad (Isatis tinctoria) and the reduction of indigo with environmentally friendly sugars. The goal is to find an environmentally friendly dyeing method suitable for home dyers and craft teaching. Indigo precursors were extracted from three different strains of woad by three slightly different steeping methods. Indigo was reduced to its water-soluble form with fructose and glucose, and control samples with sodium dithionite. The resulting indigo dye was used to dye cotton fabric. The color yield is considered in relation to the different strains of woad, extraction methods and reducing agents. In addition, the washing and abrasion resistance of the color with different strains of woad, extraction methods and reducing agents is examined. Longer extraction time and chopping of the leaves improved the dyeing result. However, in addition to indigo, chopped leaves and longer extraction time also resulted in increased amount of other colorants in the dye, as the samples were greener and more yellow than their controls. However, in laundering, these samples faded less than others and their color turned bluer as the yellow colorants washed away. Among the strains, the best color yield was obtained from the 2002 row spacing and seed quantity test conducted by the MTT Agrifood Research Finland (now known as the Natural Resources Institute Finland). There were no differences in the laundering and abrasion resistance tests between the woad strains. Indigo was successfully reduced with both fructose and glucose, but color yields were lighter and less blue than with sodium dithionite. There were no significant differences in color yield between fructose and glucose. Fructose scored slightly better than other reducing agents in laundering tests. Sugar reduction is thus well suited for both home dyeing and craft teaching, but to improve the coloring result, the woad leaves should be chopped and extracted in hot water (80 ˚C) for half an hour.