Asian blues: natural indigo sources in Asia

Before the invention of synthetic indigo, the main source for dyeing textiles blue for thousands of years was natural indigo. Indigo was appreciated for the long lasting, stable quality of its colour. The sophisticated knowledge of gaining the dye material from plants and dyeing in fermentation vats was developed all over the world by discovering and using local species from at least eight plant families. As Asia has the highest diversity of species used for gaining indigo, our research focuses on field sites in China, India, Indonesia and Laos. Literature provides a solid basis for understanding principle processing steps and species used in history. What is lacking is the detailed documentation of contemporary use of indigo yielding plants that includes all steps from cultivation to the final product. This refers especially to plants that did not gain a worldwide reputation in the past, but were widely used on a local scale. Nevertheless, we have evidence from recent local ethnobotanical inventories and our own scoping visits that these plants are still in use in remote areas. We focus on the following research questions: (1) which species yielding indigo are used today by whom and in what form?; (2) which cultivation, collection, processing and dyeing methods are applied?; and (3) which similarities and differences of the applied processing and dyeing techniques can be documented by measuring process relevant parameters? The second focus of our research is on quality. The aspect of quality is not dealt with in recent ethnobotanical research about natural indigo use. It was, however, a key factor in indigo production throughout history, is regaining significance again and will be essential for future production. Key questions are: (1) how is quality defined, measured or categorized along the indigo supply chain?; (2) how can quality be influenced throughout the supply chain?; and (3) which qualities of natural indigo are being achieved today? Hypotheses will be generated about quality influencing factors throughout the supply chain. An interdisciplinary set of methods will be applied: (1) analysis of historical documents from colonial research on indigo; (2) ethnobotanical field research in China, India, Indonesia and Laos; (3) measuring of process relevant parameters; and (4) analysis of indigo samples concerning the content of indigotin and additional components which could be relevant for quality.