 | | | | © Jérôme Johnson |
In the 17th century, Colbert issued a decree classifying tinctorial
plants in two categories, “grand teint” (colourfast) and “petit teint” (less colourfast), according to their dyeconcentration and the quality of the dyes produced– the brightness of their colours and their resistance to light and washing.
The use of natural, and especially of plant-based, colorants remained the only way to dye fibres until the discovery of synthetic colouring agents at the end of the 19th century. To dye fibres, the colorant must be soluble in water and the fibre must be prepared to receive it, with the hue selected in advance. Four operations are required: mordanting, dyeing pere, rinsing, and drying.
Mordanting prepares the fibre and enables the colours to be fixed. The fibres are boiled in a hot bath containing alum, iron sulphate or copper sulphate. A number of barks contain substances that can be used as mordants. Dyeing is carried out in a bath at high temperature (which varies according to the fibre used) and in which the plant parts (bark, leaves, flowers, etc.) have been boiled to extract the dyes.
Nevertheless, the colour of the liquor can be modified by means of oxidation or the use of copper sulphate. Fermentation (cold) dyeing, in which natural colorants are left to soak in water for several weeks, is another technique.
The colour blue is special. Its colorant (indigo), is obtained from a small number of plants such as woad and indigo tree. Since this colorant is not soluble in water, it requires a special process.
Rinsing in cold or lukewarm water is followed by drying in a dry and well-ventilated place; fibres and skeins are pressed.
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