Dyeing is the application of dyes or pigments on textile materials such as fibers, yarns, and fabrics with the goal of achieving color with desired color fastness. Dyeing is normally done in a special solution containing dyes and particular chemical material. Dye molecules are fixed to the fiber by absorption, diffusion, or bonding with temperature and time being key controlling factors. The bond between dye molecule and fiber may be strong or weak, depending on the dye used. Dyeing and printing are different applications; in printing, color is applied to a localized area with desired patterns. In dyeing, it is applied to the entire textile.
The primary source of dye, historically, has been nature, with the dyes being extracted from animals or plants. Since the mid-19th century, however, humans have produced artificial dyes to achieve a broader range of colors and to render the dyes more stable to washing and general use. Different classes of dyes are used for different types of fiber and at different stages of the textile production process, from loose fibers through yarn and cloth to complete garments.
Acrylic fibers are dyed with basic dyes, while nylon and protein fibers such as wool and silk are dyed with acid dyes, and polyester yarn is dyed with disperse dyes. Cotton is dyed with a range of dye types, including vat dyes, and modern synthetic reactive and direct dyes.
The earliest dyed flax fibers have been found in a prehistoric cave in the Republic of Georgia and date back to 34,000 BC. More evidence of textile dyeing dates back to the Neolithic period at the large Neolithic settlement at Çatalhöyük in southern Anatolia, where traces of red dyes, possibly from ocher, an iron oxide pigment derived from clay, were found. In China, dyeing with plants, barks, and insects has been traced back more than 5,000 years.:11 Early evidence of dyeing comes from Sindh province in Pakistan, where a piece of cotton dyed with a vegetable dye was recovered from the archaeological site at Mohenjo-daro (3rd millennium BCE). The dye used in this case was madder, which, along with other dyes such as indigo, was introduced to other regions through trade. Natural insect dyes such as Cochineal and kermes and plant-based dyes such as woad, indigo and madder were important elements of the economies of Asia and Europe until the discovery of man-made synthetic dyes in the mid-19th century. The first synthetic dye was William Perkin's mauveine in 1856, derived from coal tar. Alizarin, the red dye present in madder, was the first natural pigment to be duplicated synthetically in 1869, a development which led to the collapse of the market for naturally grown madder.:65 The development of new, strongly colored synthetic dyes followed quickly, and by the 1870s commercial dyeing with natural dyestuffs was disappearing.
Dyeing can be applied at various stages within the textile manufacturing process; for example, fibers may be dyed before being spun into yarns, and yarns may be dyed before being woven into fabrics. Fabrics and sometimes finished garments themselves may also be dyed. The stage at which a product is dyed varies depending on its intended end use, the cost to the manufacturer, its desired appearance, and the resources available, amongst other reasons. There are specific terms to describe these dyeing methods, such as:
The primary objective of dyeing is to apply uniform color to the substrate (fiber, yarn, or fabric) with required color fastness. Tie-dye and printing are the methods where the color is applied in a localized manner.
In the exhaust method, the dye is transported to the substrate by the dye liquor's motion. The dye is adsorbed onto the fibre surface and ideally diffuses into the whole of the fibre. Water consumption in exhaust application is higher than the continuous dyeing method. There are three corresponding ways of dyeing with the exhaust method.
In continuous method dye is transported to the substrate by passing it through the different stages but continuously. The continuous method is an innovative method where many discrete dyeing stages are combined, such as applying color, fixation and, washing off of unfixed dyes. Types of continuous dyeing are as follows
Waterless dyeing, also known as dry dyeing, is the newly developed and more sustainable dyeing method in which the dyes are applied to the substrate with the help of carbon dioxide or solutions that need less or no water compared to their counterparts.
The selection of the appropriate dyes is most important because any given dye does not apply to every type of fiber. Dyes are classified according to many parameters, such as chemical structure, affinity, application method, desired colour fastness i.e. resistance to washing, rubbing, and light. The properties may vary with different dyes. The selection of dye depends on the objective in dyeing and affinity (to which material is to be dyed). Fastness of color largely depends upon the molecular size of the dyes and the sloubility. Larger molecular size serves better washing fastness results.
Indigo dyes have a poor wash and rubbing fastness on denim (cotton), so they are used to produce washed-down effects on fabrics. In contrast, vat or reactive dyes are applied to cotton to achieve excellent washing fastness.
The next important criterion for selecting dyes is the assessment of hazards to human health and the environment. There are many dyes especially disperse dyes that may cause allergic reactions to some individuals, and the negative impact on the environment. There are national and international standards and regulations which need to comply.
The term "direct dye application" stems from some dyestuff having to be either fermented as in the case of some natural dye or chemically reduced as in the case of synthetic vat and sulfur dyes before being applied. This renders the dye soluble so that it can be absorbed by the fiber since the insoluble dye has very little substantivity to the fiber. Direct dyes, a class of dyes largely for dyeing cotton, are water-soluble and can be applied directly to the fiber from an aqueous solution. Most other classes of synthetic dye, other than vat and surface dyes, are also applied in this way.
The term may also be applied to dyeing without the use of mordants to fix the dye once it is applied. Mordants were often required to alter the hue and intensity of natural dyes and improve color fastness. Chromium salts were until recently extensively used in dyeing wool with synthetic mordant dyes. These were used for economical high color fastness dark shades such as black and navy. Environmental concerns have now restricted their use, and they have been replaced with reactive and metal complex dyes that do not require mordant.
There are many forms of yarn dyeing. Common forms are the package form and the hanks form. Cotton yarns are mostly dyed at package form, and acrylic or wool yarn are dyed at hank form. In the continuous filament industry, polyester or polyamide yarns are always dyed at package form, while viscose rayon yarns are partly dyed at hank form because of technology.
The common dyeing process of cotton yarn with reactive dyes at package form is as follows:
After this process, the dyed yarn packages are packed and delivered.
Garment dyeing is the process of dyeing fully fashioned garments subsequent to manufacturing, as opposed to the conventional method of manufacturing garments from pre-dyed fabrics.
Up until the mid-1970s the method was rarely used for commercial clothing production. It was used domestically, to overdye old, worn and faded clothes, and also by resellers of used or surplus military clothing. The first notable industrial use of the technique was made by Benetton, which garment dyed its Shetland wool knitwear.
In the mid-1970s the Bologna clothing designer Massimo Osti began experimenting with the garment dyeing technique. His experimentation over the next decade, led to the pioneering of not just the industrial use of traditional garment dyeing (dyeing simple cotton or wool garments) but, more importantly, the technique of "complex garment dyeing" which involved dyeing fully fashioned garments which had been constructed from multiple fabric or fiber types (e.g. a jacket made from both nylon and cotton, or linen, nylon and polyurethane coated cotton) in the same bath.
Up until its development by Massimo Osti (for his clothing brand C.P. Company), this technique had never been successfully industrially applied in any context. The complexity lay in developing both a practical and chemical understanding of how each fabric responded differently to the dye, how much it would shrink, how much color it would absorb, developing entirely new forms of quality control to verify possible defects in fabric before dyeing etc.
Beyond the industrial advantages of the technique (purchasing fabric in one color, white or natural, you may produce as many colors as you wish etc.), the artistic advantages of the technique were considerable and in many ways paved the way for the creation of the clothing style today known as Italian Sportswear. These advantages included
The disadvantages included:
Today, whilst garment dyeing is a diffusely employed as an industrial technique around the globe, predominantly in the production of vintage style cotton garments and by fast fashion suppliers, complex garment dyeing is still practiced almost exclusively in Italy, by a handful of premium brands and suppliers who remain committed to the art.
If things go wrong in the dyeing process, the dyer may be forced to remove the dye already applied by a process called "stripping" or discharging. This normally means destroying the dye with powerful reducing agents such as sodium hydrosulfite or oxidizing agents such as hydrogen peroxide or sodium hypochlorite. The process often risks damaging the substrate (fiber). Where possible, it is often less risky to dye the material a darker shade, with black often being the easiest or last option.