Dye

A dye can generally be described as a coloured substance that has an affinity to the substrate to which it is being applied. The dye is usually used as an aqueous solution, and may require a mordant to improve the fastness of the dye on the fibre. In contrast, a pigment generally has no affinity for the substrate, and is insoluble.

Organic dyes

The first man-made organic dye, mauveine, was discovered by William Henry Perkin in 1856. Many thousands of dyes have since been prepared and, because of vastly improved properties imparted upon the dyed materials, quickly replaced the traditional natural dyes. Dyes are now classified according to how they are used in the dyeing process.

Related Topics:
Organic - Mauveine - William Henry Perkin - 1856

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Acid dyes are water-soluble anionic dyes that are applied to fibres such as silk, wool, nylon and modified acrylic fibres using neutral to acid dyebaths. Attachment to the fibre is attributed, at least partly, to salt formation between anionic groups in the dyes and cationic groups in the fibre. Acid dyes are not substantive to cellulosic fibres.

Related Topics:
Acid dye - Water - Soluble - Anionic - Fibre - Silk - Wool - Nylon - Modified acrylic fibre - Cationic - Cellulosic

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Basic dyes are water-soluble cationic dyes that are mainly applied to acrylic fibres, but find some use for wool and silk. Usually acetic acid is added to the dyebath to help the uptake of the dye onto the fibre. Basic dyes are also used in the coloration of paper.

Related Topics:
Basic dye - Acrylic fibre - Acetic acid - Paper

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Direct or substantive dyeing is normally carried out in a neutral or slightly alkaline dyebath, at or near boiling point, with the addition of either sodium chloride (NaCl) or sodium sulfate (Na2SO4). Direct dyes are used on cotton, paper, leather, wool, silk and nylon. They are also used as pH indicators and as biological stains.

Related Topics:
Substantive dye - Alkaline - Boiling point - Sodium chloride - Sodium sulfate - Cotton - Leather - Nylon - PH indicator - Biological stain

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Mordant dyes require a mordant, which improves the fastness of the dye against water, light and perspiration. The choice of mordant is very important as different mordants can change the final colour significantly. Most natural dyes are mordant dyes and there is therefore a large literature base describing dyeing techniques. The most important mordant dyes are the synthetic mordant dyes, or chrome dyes, used for wool; these comprise some 30% of dyes used for wool, and are especially useful for black and navy shades. The mordant, potassium dichromate, is applied as an after-treatment.

Related Topics:
Mordant - Light - Perspiration - Potassium dichromate

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Vat dyes are essentially insoluble in water and incapable of dyeing fibres directly. However, reduction in alkaline liquor produces the water soluble alkali metal salt of the dye, which, in this leuco form, has an affinity for the textile fibre. Subsequent oxidation reforms the original insoluble dye.

Related Topics:
Vat dye - Alkaline liquor - Alkali metal salt - Oxidation

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Reactive dyes utilize a chromophore containing a substituent that is capable of directly reacting with the fibre substrate. The covalent bonds that attach reactive dye to natural fibers make it among the most permanent of dyes. "Cold" reactive dyes, such as Procion MX, Cibacron F, and Drimarene K, are very easy to use because the dye can be applied at room temperature. Reactive dye is by far the best choice for dyeing cotton and other cellulose fibers at home or in the art studio.

Related Topics:
Reactive dyes - Chromophore - Substituent - Reacting - Covalent - Cotton - Cellulose

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Disperse dyes were originally developed for the dyeing of cellulose acetate, and are substantially water insoluble. The dyes are finely ground in the presence of a dispersing agent and then sold as a paste, or spray-dried and sold as a powder. They can also be used to dye nylon, triacetate, polyester and acrylic fibres. In some cases, a dyeing temperature of 130 °C is required, and a pressurised dyebath is used. The very fine particle size gives a large surface area that aids dissolution to allow uptake by the fibre. The dyeing rate can be significantly influenced by the choice of dispersing agent used during the grinding.

Related Topics:
Disperse dye - Cellulose acetate - Triacetate - Polyester - Temperature - °C

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Azoic dyeing is a technique in which an insoluble azoic dye is produced directly onto or within the fibre. This is achieved by treating a fibre with both diazoic and coupling components. With suitable adjustment of dyebath conditions the two components react to produce the required insoluble azoic dye. This technique of dyeing is unique, in that the final colour is controlled by the choice of the diazoic and coupling components.

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