Plant based dyes are classified in the following ways to make it easier to understand and work with them successfully.
According to scientific literature natural dyes are classified based on the following parameters:
Chemical structure of
the dye component
Direct, in a vat, processed in acidic or basic medium
Derived from animals, plants or minerals
Asia, South America, Africa
India, South east Asia,
India, Middle East
Natural fibres are not able to absorb colours directly so they are mordanted with a metallic salt by soaking them in a salt solution for a period of time. This is a key step in the natural dyeing process, known as mordanting.
Natural fibres like cotton, silk, wool, jute, hemp, linen and leather have poor dye affinity.
Mordanting with a metallic salt forms bonds with the ions in the fibre to be dyed, that increase the dye uptake and dye affinity of that natural fiber.
Mordants are generally classified into the following:
Metallic – Salts of tin, iron, copper, ferrous and chromium. These are considered polluting and unsafe.
Non metallic / Natural - Alum, potash alum and Myrobalan seed powder or Harda
Tannins & oil – Tannins are extracted from the bark, leaves or fruits of plants. Some are oil based. For example, Turkey red oil is used as a tanning agent to get deep reds from Madder
Care needs to be taken to use safe metallic salts in natural dyeing so as to not cause harm to the environment or the dyer. Safe mordants are Harda, Alum and a few metal salts approved by the European Union.
Much research and experimentation is required to perfect dyeing techniques and shade outcomes while using natural mordants and tannins.
Plant Based Dye Production
The production of plant based dyes is a rigorous process. It needs to be carried out scientifically to beget good quality dyes from plant sources
Plant Based Dyeing Process
The dyeing process for food, pharmaceuticals, cosmetics, surface painting and surface printing is quite different from that of textile and leather colouring. Textile and leather colouring are the major applications of plant based colours segment.
The description below describes some generic steps for textile and leather colouring:
There are several steps in the plant based dyeing process, including scouring the fabric or medium to remove impurities followed by steeping it in water, Harda or the required mordanting solution
The steps vary based upon the dyestuff used, the fabric type and its weight, the specific craft method (Ajrakh, Kalamkari, Ikkat, Dabu, etc.) and the experience of the dyer. The weight of the fabric dictates the weight of the dyestuff, mordant and other essential items to be used
The intensity of colour or shade dictates the steeping time or the number of times that the medium or the yarn needs to be dipped into the colour bath or vat
Master dyers and craft-persons develop a very unique dyeing process that results in consistent, unique and durable shades for their products.
Dyes and Dyeing Glossary A Glossary of Terms for Materials and Processes in Textile Dyeing for Artists By Saidur Rahman..
Natural Dyes: Sources, Chemistry, Application and Sustainability Issues By Gowtham Nanda
Dyeing of textiles with Natural dyes, Wardha view project, By Ashish Kumar Samantha, University of Calcutta, Pub Nov 2011.
Eco-friendly dyeing of wool using natural dye from weld as co-partner with synthetic dye, by Mohammad Mirjalili, Journal of cleaner production, Pub July 2011
Read more about Plant colour