Dye Plants

To decorate the living space, objects and clothes with colour seems to be a basic human need. While mineral pigments of cave paintings have lasted up to 30,000 years the earliest textile dyes of vegetable and animal origin are about 3,000 years old. It is likely that in the Bronze Age the experimental phase of textile dyeing started simultaneously with the introduction of wool. Prehistoric man had experienced that the colours found in nature could not easily be applied to textiles. Green leaves, blue and red flowers and fruits did not provide fast textile dyes. Between 2002 and 2013 about 60 coloured textile fragments from the prehistoric mines of Hallstatt in Upper Austria were investigated. High performance liquid  chromatography with photo diode array detection (HPLC-PDA) served to analyse the dyes. Optical light microscopy and scanning electron microscopy coupled to energy-dispersive spectroscopy (SEM-EDS) were used to investigate the condition of the textiles and the dyeing procedures. The research showed that the most important dye classes and the dyeing processes underlying textile dyeing with natural dyes were known as early as in the Bronze Age and were developed further during the Iron Age. Including the dye analysis of textiles from other European sites the possibilities and limitations in identifying the dyes and the dyeing materials will be discussed. Is it possible to find out which dyeing method was used? Is it possible to conclude that dyeing material or dyed textiles have been traded? Archaeobotanical finds can provide information on the distribution and cultivation of dye plants. Among the outstanding achievements of prehistoric humans are the production of the blue pigment indigotin from the green woad leaves, and the production of purple red to blue pigments from the glands of the purple snails. Additionally it was necessary to develop an appropriate method that enables dyeing with insoluble pigments – the vat dyeing. It has been microscopically proven that wool was dyed with woad also after spinning and weaving. Brown dyeing tannins, the red lichen dye orcein and some few other dyes are suitable for direct dyeing because they bond directly to the textile fibres without any additives. Nearly all durable yellow and red colours require mordant dyeing. Yellow flavonoids were easily to discover as they occur in weld, dyer’s broom and many other plants. Red anthraquinones are rare in nature and had to be found in the rhizomes of the Rubiaceae family (e.g. bedstraw, madder) and in dye insects. Mordant dyes, also called metal complex dyes, are soluble in water and therefore have to be fixed on the fibres by means of mordants such as tannins and metal ions of aluminium, iron and copper. The metal ions form chemical bonds with the dye molecules and the fibre molecules building insoluble lakes. Which sources of metal ions could have been used in prehistory? Was it possible to dye yellow and red without mordants? Fermentation seems to be an alternative. Prehistoric people received a wide range of colours by using woad for blue, rhizomes of Rubiaceae and dye insects for red and many flavonoid containing plants for yellow. It seems that tannins were rarely used for dyeing brown but served as mordants or combined with iron-containing materials to achieve black. Green was dyed by double dyeing with woad and a yellow dyeing plant. Multi-stage dyeing processes were performed to obtain certain colour shades.