Here is a very basic overview of dyes in common use.
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. Synthetic dyes quickly replaced just about all the traditional natural dyes. They cost less, they offer a vast range of new colours, and they impart improved properties to the dyed materials.
Most dyes are now classified according to how they are used in the dyeing process.
Acid dyes are water-soluble anionic dyes that are used on fibres such as silk, wool, nylon, various other natural materials, and modified acrylic fibres ,by the use of neutral to acid dye-baths. Fibre attachment is attributed, at least in part, to the formation of salt between anionic groups in the dyes and cationic groups in the fibres. Acid dyes are not substantive to cellulose type fibres.
Basic dyes are water-soluble cationic dyes that are used mainly on acrylic fibres, but are also occasionally used for wool. silk, and some other natural materials. As a rule, acetic acid is added to the dye-bath to assist the dye uptake of the fibre Basic dyes are also used to colour paper.
Direct or substantive dyeing is normally carried out in a neutral or slightly alkaline dye-bath, at or near boiling point, and using sodium chloride (NaCl) or sodium sulfate (Na2SO4). Direct dyes are mainly used on cotton, paper, leather, wool, silk and nylon. These dyes are also often used as pH indicators and as biological stains.
Mordant dyes require a mordant, which is a substance that improves the fastness of the dye against water, light and perspiration. Mordant choice is extremely important as various mordants can change the final colour very significantly.
Most natural dyes are mordant dyes, and there is quite a lot of literature extant describing properties and techniques to be used with these dyes. Synthetic mordant dyes , or chrome dyes are the most important, mainly used for wool. About a third of the dyes used for wool are synthetic mordant dyes and are especially used for black and dark blue shades. In these cases, the mordant, potassium dichromate, is applied as an after-treatment.
Vat dyes are basically insoluble in water and not capable of dyeing fibres directly. However, reducing them in alkaline liquor produces the water soluble alkali metal salt of the dye, which, in this so called "leuco" form, has an affinity for the fibre. Subsequent oxidation reforms the original insoluble dye.
Reactive dyes rely on a chromophore containing a substituent that reacts directly with the fibre substrate. The covalent bonds that attach reactive dye to natural fibres make it one of the most permanent dyes. "Cold" reactive dyes, such as Procion MX, Cibacron F, and Drimarene K, are easy to use as the dye may be applied at room temperature. Reactive dye is the best choice for dyeing cotton, cellulose fibres, and is also extremely useful for dyeing sensitive natural materials such as Polar Bear, Arctic fox, and some others. Hot dyes damage these furs, making them more or less unusable for some purposes, fly-dressing included!
Dispersal dyes were developed for dyeing cellulose acetate, and are also essentially water insoluble. These dyes are ground to fine powder in a dispersing agent and then sold either as a paste, or spray-dried, and sold as a powder. These dyes may be used to dye nylon, triacetate, polyester and acrylic fibres. For some of these things a dyeing temperature of 130??C is necessary, and a pressurized dye bath is used. Extremely fine particle size gives a large surface area, aiding uptake by the fibre. Dyeing rates are significantly influenced by the choice of dispersing agent used during the grinding.
Azo dyeing is a technique whereby insoluble azoic dye is produced directly on or within the fibre. This is done by treating a fibre with diazoic and coupling components. Under suitable dyebath conditions the two components react and produce the desired insoluble azo dye. This dyeing technique is unique, because the final colour is controlled by the choice of the diazoic and coupling components.
One other class which describes the application role of dyes, and not their mode of use, is food dye. Food dyes are classed as food additives, they are manufactured to a higher standard than most industrial dyes. Food dyes may be direct, mordant or vat dyes, and their use is usually strictly controlled by legislation. Many of these dyes are azoic dyes, although anthraquinone and triphenylmethane compounds are used for colours such as green and blue. Some natural dyes are also used.
A number of other dye classes have also been established, including:
Sulphur Dyes for textiles
Carbene dyes for colouring multiple substrates
Oxidation bases, for mainly hair and fur
Leather dyes, for leather
Fluorescent brighteners, for textile fibres and paper
Solvent dyes, for wood staining and producing coloured lacquers, solvent inks, colouring oils, waxes.
Only a few of these are suitable for use by amateurs. Even many natural dyes use extremely poisonous and dangerous materials, and require care in use. For many sensitive materials, "cold" reactive dyes are now being used more and more. They still depend on the correct dye-bath temperature, but this is usually somewhere around 30??C, and does not present as many problems as dye baths used near or above boiling point.
Furthermore, and this will doubtless cause some controversy, some dyes in regular use are less suitable than many people imagine. RIT dye is NOT suitable for dyeing most natural materials!
I know Mr.Best recommends it, but it is not a good choice. You need to use a lot of dye, and RIT is also a so called "union" or "combination" dye which may be used on various things like proteins and cellulose, nylon, and polyester, because it contains several different types of dye. Normally, it will also not give the bright vibrant colours fly-dressers are looking for on natural materials, and a lot of dye components are simply wasted on natural materials, as they can not bond to them.
Veniard ?s dye also has a number of quite severe limitations! With few exceptions, namely hot orange, lemon yellow, scarlet, and kingfisher blue, all Veniard ?s dyes are mixed colour dyes.This causes problems with colour consistency between batches, as even if you weigh the dye powder very accurately indeed, the dye colour powder is not a homogenous mixture, and even vigorous mixing or shaking will not make it so, because the specific gravities of the various dye colours vary, and the heavier colours will sink to the bottom of the mixing vessel when stirred or shaken. Veniard??s also uses different acid dyes to obtain some colours, and these differ in molecular structure, causing varying dye rates. This can cause a number of problems!
For some materials, hot acid dyes are completely unsuitable. At the temperature required for the dye to take, Polar bear fur for instance is burned, and it loses its tips, making it useless for fly-dressing! As already stated elsewhere, prolonging the time in the bath will not make any appreciable difference to the final shade of any material. The temperature is critical. Adding more dye is also useless and will only be washed out when rinsing anyway, as it has not "taken". The temperature is absolutely critical for hot aniline dyes. Unless you reach the required temperature the dyes simply will not take properly. It does not matter what anybody else says, this is a simple fact.
When you reach the required temperature, ( which varies somewhat according to the dye bath and the materials being dyed), the dye "takes" immediately, and the dye bath clears almost as if by magic. Unless this occurs, the dye has not "taken", the colour will not be "fast", and a lot of dye will simply be rinsed out when the material is rinsed. Sorry to keep repeating this, but it is the single major cause of failure by beginners.
Some feathers and hairs curl badly, or the tips are damaged, at close to the "taking temperature" of the dye. ? When hot dyeing, the material must not be allowed to touch the sides of the dye-bath anyway, and should be constantly agitated, as long as heat is being applied. Best to withdraw the heat shortly before the material is placed in the bath. Rinse the material ( which should be clean, grease free, and completely soaked) in very hot water before placing in the dye bath. This prevents the bath cooling too much, which will prevent the dye from taking properly.
For dyeing Polar Bear, ( which I have done quite a few times now), cold reactive dyes like these, or similar are best;
http://www.dyeproservices.com/Dylon%...ater%20Dye.htm
The following is a patch of Polar bear dyed using "Primrose" from the above list of cold dyes. I just scanned the patch on a flatbed scanner, so the photo quality is not brilliant, but enough to give you the idea I hope).
Cont'd ->
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