| A dye can generally be described as a colored | | | | dichromate, is applied as an after-treatment. |
| substance that has an affinity to the | | | | It is important to note that many mordants, |
| substrate to which it is being applied. The | | | | particularly those in the hard metal |
| dye is generally applied in an aqueous | | | | category, can be hazardous to health and |
| solution, and may require a mordant to | | | | extreme care must be taken in using them. |
| improve the fastness of the dye on the fiber. | | | | |
| | | | Look up leuco form in Wiktionary, the free |
| Both dyes and pigments appear to be colored | | | | dictionary. |
| because they absorb some wavelengths of light | | | | |
| preferentially. In contrast with a dye, a | | | | Vat dyes are essentially insoluble in water |
| pigment generally is insoluble, and has no | | | | and incapable of dyeing fibres directly. |
| affinity for the substrate. Some dyes can be | | | | However, reduction in alkaline liquor |
| precipitated with an inert salt to produce a | | | | produces the water soluble alkali metal salt |
| lake pigment. | | | | of the dye, which, in this leuco form, has an |
| | | | affinity for the textile fibre. Subsequent |
| Archaeological evidence shows that, | | | | oxidation reforms the original insoluble dye. |
| particularly in India and the Middle East, | | | | |
| dyeing has been carried out for over 5000 | | | | Reactive dyes utilize a chromophore |
| years. The dyes were obtained from animal, | | | | containing a substituent that is capable of |
| vegetable or mineral origin, with no or very | | | | directly reacting with the fibre substrate. |
| little processing. By far the greatest source | | | | The covalent bonds that attach reactive dye |
| of dyes has been from the plant kingdom, | | | | to natural fibers make it among the most |
| notably roots, berries, bark, leaves and | | | | permanent of dyes. "Cold" reactive dyes, such |
| wood, but only a few have ever been used on a | | | | as Procion MX, Cibacron F, and Drimarene K, |
| commercial scale. | | | | are very easy to use because the dye can be |
| | | | applied at room temperature. Reactive dyes |
| Organic dyes | | | | are by far the best choice for dyeing cotton |
| | | | and other cellulose fibers at home or in the |
| The first human-made (synthetic) organic dye, | | | | art studio. |
| mauveine, was discovered by William Henry | | | | |
| Perkin in 1856. Many thousands of synthetic | | | | Disperse dyes were originally developed for |
| dyes have since been prepared. | | | | the dyeing of cellulose acetate, and are |
| | | | substantially water insoluble. The dyes are |
| Synthetic dyes quickly replaced the | | | | finely ground in the presence of a dispersing |
| traditional natural dyes. They cost less, | | | | agent and then sold as a paste, or |
| they offered a vast range of new colors, and | | | | spray-dried and sold as a powder. They can |
| they imparted better properties upon the dyed | | | | also be used to dye nylon, cellulose |
| materials.[1] Dyes are now classified | | | | triacetate, polyester and acrylic fibres. In |
| according to how they are used in the dyeing | | | | some cases, a dyeing temperature of 130 °C |
| process. | | | | is required, and a pressurised dyebath is |
| | | | used. The very fine particle size gives a |
| Acid dyes are water-soluble anionic dyes that | | | | large surface area that aids dissolution to |
| are applied to fibers such as silk, wool, | | | | allow uptake by the fibre. The dyeing rate |
| nylon and modified acrylic fibers using | | | | can be significantly influenced by the choice |
| neutral to acid dyebaths. Attachment to the | | | | of dispersing agent used during the grinding. |
| fiber is attributed, at least partly, to salt | | | | |
| formation between anionic groups in the dyes | | | | Azo dyeing is a technique in which an |
| and cationic groups in the fiber. Acid dyes | | | | insoluble azoic dye is produced directly onto |
| are not substantive to cellulosic fibers. | | | | or within the fibre. This is achieved by |
| | | | treating a fibre with both diazoic and |
| Basic dyes are water-soluble cationic dyes | | | | coupling components. With suitable adjustment |
| that are mainly applied to acrylic fibers, | | | | of dyebath conditions the two components |
| but find some use for wool and silk. Usually | | | | react to produce the required insoluble azo |
| acetic acid is added to the dyebath to help | | | | dye. This technique of dyeing is unique, in |
| the uptake of the dye onto the fiber. Basic | | | | that the final color is controlled by the |
| dyes are also used in the coloration of | | | | choice of the diazoic and coupling |
| paper. | | | | components. |
| | | | |
| Direct or substantive dyeing is normally | | | | Sulfur dyes are two part "developed" dyes |
| carried out in a neutral or slightly alkaline | | | | used to dye cotton with dark colors. The |
| dyebath, at or near boiling point, with the | | | | initial bath imparts a yellow or pale |
| addition of either sodium chloride (NaCl) or | | | | chartreuse color. This is oxidized in place |
| sodium sulfate (Na2SO4). Direct dyes are used | | | | to produce the dark black we are familiar |
| on cotton, paper, leather, wool, silk and | | | | with in socks and the indigo blue of the |
| nylon. They are also used as pH indicators | | | | common blue jeans. |
| and as biological stains. | | | | |
| | | | Food dyes |
| Mordant dyes require a mordant, which | | | | |
| improves the fastness of the dye against | | | | One other class which describes the role of |
| water, light and perspiration. The choice of | | | | dyes, rather than their mode of use, is the |
| mordant is very important as different | | | | food dye. Because food dyes are classed as |
| mordants can change the final color | | | | food additives, they are manufactured to a |
| significantly. Most natural dyes are mordant | | | | higher standard than some industrial dyes. |
| dyes and there is therefore a large | | | | Food dyes can be direct, mordant and vat |
| literature base describing dyeing techniques. | | | | dyes, and their use is strictly controlled by |
| The most important mordant dyes are the | | | | legislation. Many are azoic dyes, although |
| synthetic mordant dyes, or chrome dyes, used | | | | anthraquinone and triphenylmethane compounds |
| for wool; these comprise some 30% of dyes | | | | are used for colors such as green and blue. |
| used for wool, and are especially useful for | | | | Some naturally-occurring dyes are also used. |
| black and navy shades. The mordant, potassium | | | | |