CRITICAL PROCESSES Ltd

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PRODUCTION OF INDIGO FROM WOAD

The traditional production of indigo from indigoferous plants such as woad, is a long-winded and labour-intensive process. It is still carried out in some parts of the world. Then, in the nineteenth century, indigo was synthesised and most of it is now produced synthetically. In recent years more emphasis has been placed on greener and more sustainable processes, so we have looked for a method, with a number of European partners, of producing indigo sustainably from plants more quickly and efficiently.

In the process developed, the indigo precursors are extracted from woad using hot water. The extract is filtered and treated with air in alkaline conditions (from lime) to produce the insoluble indigo. This is allowed to settle and filtered off. In the traditional process an enzyme present in the plant converts the precursors to indigo in shallow pools with agitation over a period of 3 days, whereas the new process takes 10 minutes.

The small production plant now being used in Italy is shown above. It can process 5 tons of woad per day which will give up to 20 kg of indigo. The indigo produced has been used in a number of fashion shows, such as one in Finland, with an example shown below.

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