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