Natural dyes can be classified as either adjective or substantive. Most dyes are adjective which means they require a mordant to help bind the color to the fiber. They will dye without mordant but the color will not be as fast (ie. wash fast or light fast).
Substantive natural dyes are those that do not require a mordant to hold the color. This list includes lichens, safflower, turmeric and indigo. Indigo can be further classified as a natural vat dye. It does not require a mordant but does require a special process of reduction / oxidation in order to adhere to the fiber. While substantive dyes do not require a mordant, mordants can still be useful to increase the color and shade range of the natural dye plant.
Direct dyeing is a term sometimes used to describe a substantive natural dye, ie. one that does not require a mordant. But it is also a term commonly used in regards to synthetic dyes. It simply means the color will adhere directly to the fiber.
Natural dyes can come from various parts of a plant - the flower, the berry, the leaves, branches or roots or from the bark, wood or cones. Flowers can be used as they are or crushed. Berries should be crushed. Leaves, branches, and roots (or rhizomes) should be chopped as finely as possible and allowed to soak in lukewarm water for 12 hours, then heated and boiled for 1-2 hours. Wood, bark and cones should be in the form of woodchips, sawdust or crushed and soaked for 3 days before slowly heating and boiling for 2-3 hours. Plant material should then be strained out and the dyebath cooled to room temperature. Pre-wetted, mordanted fiber can then be added to the dyebath.
Natural dyes can be purchased in a couple of different forms such as dried, powdered, fermented or extract. The most common is simply the dried natural plant material in a crushed or powdered form. The woodier dried material should still be pre-soaked for 1-3 days.
Technically, a dye bath made from plant material is a natural extract, that is you are 'extracting' the coloring component of the plant. But commercially, an extract is usually used to refer to a very concentrated form of the dyes. A dye bath has already been produced, then this liquor is evaporated down to a concentrate using specialized equipment. Natural extracts are considerably more expensive but a little goes a long way. It is space efficient to store extracts and because they dissolve completely in water there is no need to strain out plant material from the bath or rinse it from the fiber. But if they are only going to be diluted back into a dye bath, they may not be worth the extra expense to you. The real advantage to extracts is that they can be used for painting on fabrics or yarns. Extracts are available from Earthues, Maiwa, Aurora Silk and Wild Colours.
Dried fermented natural dyes, as sold by Blue Castle Fiber Arts, are somewhere between dried plant materials and extracts. The colors are more concentrated than the simple dried but the cost is within the same range - unless of course, you collect your own plants. The fermentation process is natural, eco-friendly and allows different dye plants to be combined into one color - giving beautiful shades and very satisfactory color fastness. It also allows for two of the indigo based colors, Navy Blue and Forest Green to be used easily on wool and silk without the indigo vat method (although these two dyes will not work on cellulose fibers). Depending on the color, the dried material is either in a granular or a fine powder form. Like the other dried materials, there will be some plant "stuff" left to be strained from the pot or rinsed from the fiber.
All natural dyes, whether dried, fermented or extract form, can be combined to obtain different colors and shades. They can also all be used with the various mordants to further stretch the color range.
The term 'mordant' derives from a french word meaning 'to bite' the fiber - describing how mordants were thought to work. In reality, it is still not really understood how they help dye adhere better to fiber. Most mordants are mineral salts, the most common being salts of aluminum, iron, copper, tin and chrome. The use of some of these mordants have led to the criticism that natural dyeing can be as toxic to the environment as synthetic dyes. Alum (aluminum sulphate) and iron (ferrous sulphate) are considered very low toxicity while tin, copper and chrome in particular (stannous chloride, copper sulphate and potassium dichromate) are considerably more toxic. Some defend their use for the small hobbyist since the amount used is quite minuscule but their use should be seriously considered for any larger scale natural dye operation.
The most important non-mineral natural mordant is tannic acid which is extracted from plants high in tannins, usually tara pods, gallnuts or sumac. The plant Myrobalan is also very high in tannins and is used as both a yellow dye and a natural plant mordant. It is the basis of the Herbal Mordant you can purchase from Blue Castle Fiber Arts. As a mordant, only a small amount is used so it only gives a slight yellow tinge to the fiber. Tannic acid/ tannins are the most environmentally friendly of the mordants. When mordanting natural cellulose fibers like cotton, a tannin should be used before a metal mordant like alum which then binds well to the fiber-tannin complex. Other non-mineral mordants historically used included urine and blood.
There are a couple ways to use mordants in the dyeing process: premordanting, simultaneous mordanting and post-mordanting. Premordanting is the most common. The fiber is prepared with the mordant and can either be dyed immediately or stored wet (temporarily) or dried until ready to dye. Simultaneous mordanting is used less often. In this case the mordant is added to the dye bath before the fiber is added. In post-mordanting, the fiber is removed from the dye bath, the mordant is added in, sometimes very gradually until a desired shade is reached, then the fiber is returned to the dyebath. The post-mordant can be a second mordant. For example, the fiber may be premordanted with alum and then post-mordanted with another mordant such as iron or copper. The purpose is to attain yet another range of colors. The iron or copper in this case are sometimes referred to as modifiers.
Modifier more often refers to a substance used to alter the pH of the dye bath. For example, vinegar or citric acid will lower the pH (make it more acidic) whereas sodium bicarbonate, sodium carbonate (washing soda) or ammonia will raise the pH (make more alkaline). The pH of a natural dye bath can have a significant effect on the color of a bath. Also, wool and silk tend to dye better in a more acidic bath while the cellulose fibers do better in an alkaline bath. Extremes on either end of the pH scale can damage fibers and should be avoided.
Blue Castle Fiber Arts is a small on-line fiber arts business and importer of natural dyes from India. We are located on the beautiful shores of Lake Ontario in Hamilton, Ontario, Canada.
This website focuses on our easy-to-use natural dyes and you will find plenty of information about them and how to use them. You can also visit our supplier's website here: Sam Vegetable Colours.