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Indigo

Indigo is a deep blue shade. Indigo extracted of plants was a product known for thousands of years in the Far East. However, indigo has not been produced industrially until the latter half of the 19th century. There are a countless number of Indigo plants (Indigofera). Innumerable different species grow wild e.g. in India, Japan and South America.

In Europe, indigo has been extracted of woad since the Stone Age. The blue of woad is not as deep as that of the indigo plant, but its fastness is better. In the Middle Ages, woad was grown in many areas, and still the 1940's, there were some woad plantations on the river Rhine. In Finland, woad has been grown mainly on the seashores of southern and southwestern Finland.

The extraction of the dye was arduous work and required carefulness. The dye is not water-soluble and therefore it must be dissolved with chemicals. In addition, the color does not fasten in the yarns when in the dye solution, but only when the yarns are removed from it. The yellowish-green color of the dye bath then turns blue due to the influence of oxygen.

Formerly, other means were used to extract the color: the blue of woad was dissolved to human urine. (The urine of a sturdy man, preferably one who had drunken the previous night, was considered the best.) This method was affordable and did not damage the yarn. A disadvantage was the smell, but it could be dissipated with ventilation and careful washing.

A recipe for extracting indigo, from Italy of the Middle Ages: "Take a bunch of fresh woad leaves and chop them well. Put the chopped woad in a sunny place, let it stand there for several days and moisten it every day with urine, until it has completely gone bad and there are big blue maggots on it. Smash the maggots and let the extract flow through a thin linen cloth to a container. Let it stand until it begins to thicken. Then form a flat cake of it and put it in an airy place to dry."