This hub starts a series of several hubs dedicated to plants that were the sources of several dyes of considerable economic importance. We will look into the methods of extraction and dyeing and their influence on society. The fascination of mankind with colours, produced by nature, goes back several millennia and from the very beginning it led people to apply them on their skin or to use them as dyes on textiles or ceramic. For some periods their importance was such that the process of extraction of dyes from plants and animals made an integral part of human life and became a very important economic activity in various cultures and civilizations. The colouring substances were obtained from several plant parts from flowers, seeds, fruits, bark, wood or roots through various physical and chemical processes. In the end, the goal was to obtain a substance soluble in a liquid were the material to be dyed was mostly immersed or painted with. The colours thus obtained directly from nature could be divided into two categories: the very expensive ones, from very rare sources or needing much elaborated extraction and fixation processes; and the less expensive, easily obtainable by extraction from local flora or fauna. The most requested and coveted colours, thus synonyms of high social status, were purple, blue and certain shades of red. Wearing these colours required skilled weavers and craftsmen with high knowledge of the methods of extraction and fixation, usually kept secret, that were being passed between generations of dyers. Thus, time-consuming and extensive dyeing processes and the need of skilled labour, which most often led to mixed results, where among the factors that influenced the colour of medieval and renaissance clothing. Therefore, while the lower classes had access to a variety of colours from cheaper plant sources existing in their local flora, red, purple, and the majority of shades of blue were not certainly among them. On the other hand, green, pink, orange, gray, yellow or gold were the most commonly used by them. The culture and the trade of rare plants and animals, as well as precious colorants, have always had an enormous socio-economic importance to many communities around the world. The processes used for staining were artisanal and semi-industrial and were performed according to established standards that determined which plants should be used for obtaining a certain colour. With time, it then became possible to produce a wide range of colours, from the same natural colouring substances, by using different metal salts, extending the use and control of colouring in art, crafts, rituals, and in many daily life situations. In this series, we will focus on the more common dyes and their plant sources, between the sixteenth and eighteenth centuries, in Europe. These plants, belonging to very different families, had great importance in the economy of that time.
Madder: History of Its Use
The art of dyeing with common madder, also known as Indian madder (Rubia cordifolia L.) seems to have originated in the East. Through the Egyptian and Persian empires, it reached the Graeco-Roman civilization. Madder is the common name given to various species of genus Rubia, with about 80 species belonging to the madder family, Rubiaceae. They are herbaceous perennial scrambling or climbing plants, with whorled leaves and small panicled flowers succeeded by red to dark berries, from which the roots of several species have been exploited as sources of dyes for textiles mostly. Rubia sp are distributed worldwide but they are mostly concentrated in South-West Europe and Central Asia. Apart from the Asian species, Indian madder, Rubia cordifolia L., European madder, Rubia tinctorum L., was the most important for commercial production, thus dye quality. Rubia tinctorum L., dyer’s madder, also called common madder, is the source of the famous Rose madder. Madder, Rubia cordifolia L., was very popular in the Middle East and Mediterranean region. It has been found in Egyptian tombs,in the ruins of Pompeii and ancient Corinth, and in Judea. However, the most ancient records date back from 3000 BC in India from pieces of cotton dyed with madder.
On growing the plant, in order to increase the content of dye, efforts were made to increase the volume of its roots, which depends not only on the plant species, but also on the type of soil. Alkaline soils are more suited to obtain a high concentration of dye in the roots. Thus, lime was added to soil to increase its content in calcium. This factor was of such importance that, for example, in the Netherlands the cultivation of madder, Rubia tinctorum L., was strictly regulated. In the Middle Ages, Charlemagne encouraged madder cultivation and madder was widely used as a dye in Western Europe in the Late Medieval centuries. While in Spain, madder was introduced and then cultivated by the Moors. The dye extracted from madder allowed obtaining bright and deep red fabrics, especially from cotton and linen fibres. This dye was known as Turkey red, first developed in India and then spread to Greece and Anatolia (Turkey), hence its name. In the multi-step dyeing process, calcium was incorporated in the dye resulting in an outstanding red colour unmatched by other shades of red obtained from other pigments. For many years the production of Turkey red remained in the hands of the Ottoman Empire until Greek workers, familiar with the methods of its production, were brought to France in 1747. Not so long after Dutch and English spies soon discovered the secret and its production was diversified. In Portugal, the red dye extracted from madder was also added to the dye extracted from brazilwood to obtain different shades of red. Apart from its economic importance as dyestuff, madder was also used in herbal medicine and was popular for treating many ailments and conditions such as jaundice, obstruction of the spleen, melancholy, palsy, haemorrhoids, sciatica, late menstrual bleeding and bruises.
The Extraction and Dyeing Processes
After harvest, the roots were dried in large deposits supplied with hot air. Roots were pealed and the tissue layer containing the dye was ground, pressed and sieved. Thereafter, various grades of dye of different particle sizes, more or less fine, were available. The ones with best quality were those in which the roots woody bark was removed. The dried roots without this treatment composed a secondary category. The residues of the separation process were also sold as lower quality dye. The roots of the European madder, Rubia tinctorum L., have a complex mixture of substances in which the acid ruberthyrin is the major component. After treatment, it decomposes to glucose, alizarin, the main pigment, and purpurin. Just out of curiosity, alizarin was the first natural pigment to be synthesized in 1868 by the German chemists Carl Graebe and Carl Liebermann, who found a way to produce it from anthracene, an aromatic hydrocarbon found in coal-tar. Ultimately, this led to the end of the economic importance of madder and its rapid disappeared from the market. Just before the synthesis of alizarin, natural rose madder supplied half the world with red in 1868. However, today madder is still cultivated and rose madder is still manufactured in traditional ways to meet the demands of the fine art market. Alizarin is also present in other species of Rubiaceae of the genera Rubia, Galium, Relbunium, Morinda and Oldenlandia, which have thus been used as sources of dyes throughout the world. Normally, purpurin is not coloured, but it becomes red when dissolved in alkaline solutions. Mixed with clay and treated with alum and ammonia, it gives a brilliant red colorant called madder lake.
The dyes extracted from the various species of Rubia belong to the group of dyes that need a mordant pre-treatment in order to fix them on cloths. The most used mordants are metal salts, alum and some iron compounds. In many procedures the use of calcium salts was recommended, especially when trying to achieve a faster colour and increased brightness. Alizarin causes an intense red colour after conversion into an insoluble lacquer by the addition of alum or a base. The addition of different mordants for dyeing madder on wool, silk, cotton or linen allows obtaining various colours that go from pink, orange, purple and brown. For example, from the application of aluminium salts reddish blue could be obtained, while adding copper salts resulted into dark purple. Tin salts or alum produced yellow orange while copper mordant produced dark orange red.
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