Very important component of the natural dyeing process is the mordant. Dyes do not interact directly with the materials they are intended to colour. Natural dyes are substantive and require a mordant to fix to the fabric, and prevent the colour from either fading with exposure to light or washing out. These compounds bind the natural dyes to the fabrics. Mordant is an intermediary agent, combining with certain natural dyes to bind the colouring matter to the fibre. A mordant is an element which aids the chemical reaction that takes place between the dye and the fibre, so that the dye is absorbed. Containers used for dying must be non-reactive (enamel, stainless steel). Brass, copper or iron pots will do their own mordanting. Different mordants yield different colours in the same dye bath; while vegetable dyes yield warm, subtle colours, their density and colour fastness are determined by varying concentrations and skilful manipulation of the mordants. Not all dyes need mordants to help them adhere to fabric. If they need no mordants, such as lichens and walnut hulls, they are called substantive dyes. If they need a mordant, they are called adjective dyes. Common mordants are alum (usually used with cream of tartar, which helps evenness and brightens slightly); iron (or copper) (which saddens or darken colours, bringing out green shades); tin (usually used with cream of tartar, which blooms or brightens col-ours, especially reds, oranges and yellows), and blue vitriol (which saddens colours and brings out greens shades). There are three types of mordant: Metallic mordants: Metal salts of aluminium, chromium, iron, copper and tin are used. Tannins: Myrobalan and sumach are commonly used in the textile industry. Oil mordants: These are mainly used in dyeing turkey red colour from madder. The main function of the oil mordant is to form a complex with alum used as the main mordent.
Mordants and Assistants
- Potassium Alum: The standard alum mordant: potassium aluminum sulfate,, hydrated. Granular form, easy to handle.
- Calcium Carbonate – Finely ground limestone – low magnesium – high calcium.
- Calcium Hydroxide – AKA hydrated or slaked lime. High purity – low in magnesium. Highly alkaline – handle with care.
- Citric Acid – Safe acid fixative for wool fibers and acid mediums. Granular, dissolves in water.
- Copper Sulfate – The standard copper mordant: cupric sulfate pentahydrate; common name: blue vitriol. Poisonous Handle with care, see warning label.
- Cream of Tartar – Potassium bitartrate; dye assistant most often used with alum and tin mordants on wool and silk.
- Ferrous Sulfate – The standard iron mordant: ferrous sulfate heptahydrate; common names are copperas and green vitriol. Poisonous: Handle with care, see warning label.
- Soda Ash – Anhydrous sodium carbonate; Chemically the same as washing or sal soda, but 2.5 times stronger. Highly alkaline; handle with care
- Sodium Sulfate, Anhydrous – Chemically the same as glauber’s salts, except more concentrated (2 1/4 times stronger).
- Spectralite®: A brand name for thiourea dioxide; used as a reducing agent in indigo dye vats; and as a bleach (stripping agent) to remove some kinds of synthetic dyes. Strong reducing agent, handle with care.
- Tara Powder: Ground seed pods of the plant Caesalpinia spinosa; about 50% tannin; a good neutral-colored source of tannin for mordanting cotton, logwood blacks, etc
- Tartaric Acid: Chemically similar to cream of tartar, but shifts pH more toward acidic.
- Tin (Stannous Chloride): Caustic, handle with care, see warning label.
- Zinc Dust:Finely powdered zinc metal. Flammable, toxic if ingested. Store away from acids & oxidizing agents
Mordents such as alum, chrome, copper sulphate, ferrous sulphate, cream of tartar, stannous chloride, tartaric acid are used as mordants. Threebasic methods of mordanting are in vogue on yarns/fabrics. The use of different mordants change the colour of same dyestuff. Thus different combination of mordants.
In this method the yarn/fabric is mordanted in the first stage and then
dyed in the second stage.
Prepare an aqueous solution by dissolving required amount of suitable
Mordant in water.
Enter the yarn/fabric and boil for 30 to 45 minutes
Dye the yarn/fabric in the prepared dyebath
Wash, rinse and dry
ii Simultaneous Mordanting
In this method the mordant and the dye are applied simultaneously in the
Record the optical density of the extracted dye liquor. Dip the yarn/fabric
in the extracted dye liquor and boil for 15 minutes.
Add required amount of mordant to the extracted dye solution and stir well
and boil for 30 to 45 minutes.
Record the optical density of the dye liquor
Wash, rinse and dry
Boil the dyed material in the mordanting liquid for 30 to 40 minutes
iii Post Mordanting:
In this method the fabric is first dyed and then mordanted.
Prepare the dye soluttion and record the optical density
Dye the yarn/fabric in the dye solution
Record the optical density of the dye liquor after dyeing
Prepare the aqueous solution by adding required amount of suitable mordant.
Boil the dyed material in the mordanting liquor for 30 to 45 minutes.
Wash, rinse and dry