Total Views : 707 , Today Views : 1
Name of Notes : – Natural Dyes Lecture Note
Natural dyes are dyes or colorants derived from plants, invertebrates, or minerals. The majority of natural dyes are vegetable dyes from plant sources—roots, berries, bark, leaves, and wood—and other biological sources such as fungi.
Archaeologists have found evidence of textile dyeing dating back to the Neolithic period. In China, dyeing with plants, barks and insects has been traced back more than 5,000 years. The essential process of dyeing changed little over time. Typically, the dye material is put in a pot of water and heated to extract the dye compounds into solution with the water. Then the textiles to be dyed are added to the pot, and held at heat until the desired color is achieved. Textile fibre may be dyed before spinning or weaving (“dyed in the wool”), after spinning (“yarn-dyed”) or after weaving (“piece-dyed”). Many natural dyes require the use of substances called mordents to bind the dye to the textile fibres. Mordents (from the Latin verb ‘mordere’, meaning ‘to bite’) are metal salts that can form a stable molecular coordination complex with both natural dyes and natural fibres.
Historically, the most common mordents were alum (potassium aluminum sulphate – a metal salt of aluminum) and iron (ferrous sulphate). Many other metal salt mordents were also used, but are seldom used now due to modern research evidence of their extreme toxicity either to human health, ecological health, or both. These include salts of metals such as chrome, copper, tin, lead, and others. In addition, a number of non-metal salt substances can be used to assist with the molecular bonding of natural dyes to natural fibres – either on their own, or in combination with metal salt mordents – including tannin from oak galls and a range of other plants/plant parts, ‘pseudo-tannins’, such as plant-derived oxalic acid, and ammonia from stale urine.
Plants that bio-accumulate aluminum have also been used, including club mosses, which were commonly used in parts of Europe, but are now endangered in many areas. The Symplocos genus of plants, which grows in semi-tropical regions, also bio accumulates aluminum, and is still popular with natural dyers. Some mordents, and some dyes themselves, produce strong odors, and large-scale dye works were often isolated in their own districts.
Modules / Lectures
- Natural Dyes and Structure
- How safe is Natural dye
- Evaluation of Dyestuff
- Basics of Natural dyeing
- Different Natural dyes
- Synthetic Dyes and dyeing
- Utilization of Natural dyes