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Article #1: What are dyes

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






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