Basic Knowledge on Textile Engineering

L/C discussion:
Stands for Letter of Credit
Types: 2 types
01. Master L/C (That from Buyers)
01. Back to Back L/C (L/C that opened against Master L/C for Fabrics, Accessories, Wash & Embroidery payment by manufacturers)
Pls everyone share your intelligence here for learning ourselves.

Working Procedures of a Woven Garments Merchandiser:

Introduction:
Garments merchandising is totally depends on time scheduling. A merchandiser is too much efficient who can deliver his order in timely. Time scheduling plays an important role through the all processes. As a result, every merchandiser has to follow a working procedure. If the working procedure is perfect then it will easy to respect the shipment date of an order.
Working procedures of a woven merchandiser:
The main working procedures of a woven garments merchandiser are discussed in the below:
There are two important key factors for proper working procedure of a woven garments merchandiser. By following it properly, anyone can touch his/her target very easily.
Fabrics follow up:
The first and most important one is “Fabrics follow up” and the second one is “Order ex*****on”. Among two key points, now I will discuss about the very first important thing named “Fabric follow up”.
Fabric follow up contains the following issues:
Fabric booking and Requisition,
Fabric in-housed,
Local accessories booking,
Accessories development,
Accessories approval.
All the main five key factors for the “fabric follow-up” are discussed in the below:
1. Fabric booking and Requisition:
When the buyer forward his/her sample with all the details instruction, in that time a woven garments merchandiser should be done fabric booking and requisition by following the buyer’s instruction about the types of fabric that he/she advised such as-Cotton denim, Spandex denim, Slub denim, 2/1 RHT etc and also on the basis of order quantity.
2. Fabric in-housed:
After completing the fabric booking, a woven garments merchandiser should arrange the accurate fabric as per buyer’s instruction and also in-hosed those before the print and embroidery approval (if there’s any print and embroidery instruction).
3. Local accessories booking:
After completing all the above two steps, a merchandiser should confirm the local accessories booking such as-Sewing thread, Zipper, Button, Metal Rivet etc. and in-house those before staring the Sewing process.
4. Accessories development:
As per order specification, if there’s needed any accessories development such as-Logo button, Logo rivet, Logo zipper puller, all types of label etc. then those should be needed to develop with urgent basis.
5. Accessories approval:
After completing the accessories development, these should be sent to the buyer for approval. When the merchandiser received the approval of those accessories then he should managed the required amount of accessories before starting the sewing process. Here one thing should be noted that, if you are not able to manage all the local accessories before sewing, you cannot control all the next processes in your own way. It’s a very important tips for a garments merchandiser.
Order ex*****on:
The second important matter to send the shipment in timely is “Order ex*****on”
Order ex*****on contains the following features:
Pattern making,
Print and embroidery development,
Fit sample making,
Wash development,
Wash approval,
Comments,
P.P sample making,
Cutting the fabric,
Print and embroidery,
Sewing,
Complete the washing process,
Finishing and QC check,
Shipment
The above all thirteen features are discussed in the below:
1. Pattern making:
After receiving all the details from the buyer, a merchandiser should pass urgently the entire reference sample with buyer’s details instruction to the pattern section for making pattern.
2. Print and embroidery development:
If there are any print and embroidery, then it should be developed with urgent basis by maintaining buyer’s instruction.
3. Fit sample making:
In the meantime, a merchandiser should make the fit sample by maintaining buyer’s instruction. Here one thing should be noted that, in fit sample, the using fabric may b varies than buyer nominated fabric, color may be varies than buyer nominated color, but measurement must be accurate as per buyers providing measurement sheet.
4. Wash development:
In woven merchandising, washing procedure is very important. Washing process is the heart of woven garments such as-Denim, twill etc. So it’s needed an extra care in this process though it’s a time killing process. Here a woven garments merchandiser should develop the wash process as per buyer’s instruction.
5. Wash approval:
After developing the washing process, it should be approved by the buyer with urgent basis. Because it has seen that a sample has to develop several times due to its different shade than buyer providing original. Here one thing should be noted that less time needed for wash approval, easy to complete rest of the process.
6. Comments:
After making the fit sample it should send to the buyer for their comments. When the buyer makes comment on fit sample, it must be noted and following their comments for next steps.
7. P.P sample making:
P.P sample means pre-production sample. It’s the approved sample for the production. P.P sample should be made as per buyer’s instruction. Here all are actual. All comments must be maintained accurately. After making P.P sample it should sent to the buyer for approval. After receiving P. P approval, a merchandiser can easily goes to production.
8. Cutting the fabric:
When the comments are received from the buyer, a woven garments merchandiser should cut the fabrics for required quantity by following buyer’s comments.
9. Print and embroidery:
After cutting the fabric, the required cutting pieces should send to print and embroidery section with buyer’s comments about the print and embroidery and completed it with urgent basis.
10. Sewing:
After completing the print and embroidery process, all the cutting pieces should be input in sewing section with buyer’s comments about the sewing.
11. Complete the washing process:
After completing the sewing process, a woven garments merchandiser should send all the garments to the washing plant and follow-up it with buyer’s instruction.
12. Finishing and QC check:
When the washing procedure will complete then merchandiser must be hand over all the garments to the finishing section. After finishing, all the garments sent to the QC (Quality Controller) department.
13. Shipment:
When the QC department approved the quality then these are sent to the buyer by sea or air.

Enzyme Wash:
The enzyme is a living biochemical substances and it works as a catalyst in the washing process. In the washing process at first step enzyme hydrolysis the cellulose and remove the projecting fibers from yarn, therefore faded effects are found by this wash. For getting proper fading effect on garments, enzyme wash is a most essential wash in the garment industry. Now I would like to discuss about this washing step and procedure of enzyme wash.
Process of Enzyme Wash:
There are two types of enzyme are used in the garment washing process. One is neutral enzyme and another is acid enzyme. Neutral enzyme is working in pH 6.5 to 7.5 on the other hand acid, enzyme works in pH 4.5 to 5.5 Enzyme is a living bio-chemical and also sensitive which is not alive below 15 °c and above 55 °c. The total washing process of enzyme wash is done in four steps. Which are discarded as following-
Desizing
Bio-abrasion
Back was
Additional Bleaching

Action of enzyme on yarn
Here I try to discuss about washing process of denim garments and weight of garments is 50 kg.
First Step (Desizing):


Desizing is the first step of enzyme wash. This step is use for removing dirt, dust and other foreign martials from garments surface. Here also using wetting agent to hard the garments.
Water add @ L: R = 1: 5
Run the machine.
Desizing agent add @ 0.5 to 2 mg / liter.
Wetting agent add @ 0.2 to 0.5 mg / liter.
Temperature: 50°c to 70°c.
Time: 10 to 15 minute.
Drop the liquor.
Cold Wash.
Second Step (Bio-abrasion):
In this step hairy fibers are removed and coloring materials are also removed by the activity of enzyme. If more fading is required then stone has to be used at half the volume of garments.
Water add @ L: R = 1: 5
Run the machine.
Anti back staining add @ 0.2 to 2 mg / liter.
Acid Enzyme add @ 0.6 to 2%
pH for acid enzyme” 4.5 to 5.5
Temperature: 45°c to 55°c.
Time: 40 to 95 minute.
Drop the liquor.
Cold Wash.
Third Steps (Back Wash):
This step is done to resist the activity of enzyme. In this step all the enzyme be dead due to high temperature. Then this dead enzymes and coloring material and other impurities are removed from the garments by dropping the liquor and dye again a rise wash by following process.
Water add @ L: R = 1: 5
Run the machine.
Anti back staining add @ 1 to 3 mg / liter.
Soda ash add @ 0.3 mg / liter.
Temperature: 70°c to 80°c.
Time: 5 to 10 minute.
Drop the liquor.
Rinse Wash.
Forth Step (Additional Bleaching):
This step is not mandatory part of enzyme wash. In this process garments be more faded. If any further fading effect is required then this step is done by following process. In this stage use sodium Meta bi-sulphite which help to resist yellow effect on garments.
Water add @ L: R = 1: 5
Run the machine.
sodium Meta bi-sulphite add @ 1 to 2 mg / liter.
Sodium hypochlorite add @ 0.5 to 5 mg / liter.
Temperature: 40°c to 50°c.
Time: 10 to 20 minute.
Drop the liquor.
Normal Wash
After Appling the above washing process drop the liquor and unload the garments and hydro extracted. At last garments are dried by gas dryer or steam dryer. If any other wash is required from the buyer then this garment is subjected to the other washing process.

VSUAL MERCHNDISING:
Merchandising is purely an aesthetics of science and its the backbone of Retail Industry. Visual Merchandising plays a highly major role in Retail Industry. However the merchandise hardly sells in retails where identical merchandise is flooded in the market. Visual Merchandising is a silent selling technique that helps to reduce the employee mix and increase per square feet returns and can further helps in reducing marketing budgets. The activity and profession of developing the floor plans and three-dimensional displays in order to maximize sales.

Both goods or services can be displayed to highlight their features and benefits. The purpose of such visual merchandising is to attract, engage, and motivate the customer towards making a purchase.

Visual merchandising commonly occurs in retail spaces such as retail stores and trade shows.

History:

When the giant nineteenth century dry goods establishments like Marshall Field & Co. shifted their business from wholesale to retail, the visual display of goods became necessary to attract the general consumers. The store windows were often used to attractively display the store’s merchandise. Over time, the design aesthetic used in window displays moved indoors and became part of the overall interior store design, eventually reducing the use of display windows in many suburban malls.

In the twentieth century, well-known artists such as Salvador Dalí and Andy Warhol created window displays.

In the beginning of twenty-first century visual merchandising is forming as a sсience. Now a days, Visual Merchandising became one of the major tool of business promotion which is widely used to attract customers and increase sales.

Techniques & Tools:

Techniques: Visual merchandising builds upon or augments the retail design of a store. It is one of the final stages in setting out a store in a way customers find attractive and appealing.

Many elements can be used by visual merchandisers in creating displays including color, lighting, space, product information, sensory inputs (such as smell, touch, and sound), as well as technologies such as digital displays and interactive installations.

As methods of visual merchandising can be used color and style, symmetry and rhythm, face and side presentation etc.

Tools: A floor map helps visual merchandisers to find the best place for garments, color stories of clothes and footwear in the shop. It is a kind offloor plan with merchandise marked.

Photo courtesy: Wikipedia
Photo courtesy: Wikipedia
Retailing in Bangladesh: Bangladesh is about more than 16 core people market. Earlier in BD there was traditional retailing in market place or sellers used to door to door marketing & selling. But now a days with the global changes BD retail market & sales idea becomes in change. That’s why so many employment has been created for the new generation & business idea been changed here. Visual merchandising is the one of new implementation here for retail business specially in apparel industry.The main reason of growth of apparel industry in spite of country being hit by recession are changing of fashion trends , rise of urbanization , growth of consumer class who understands fashion etc. But the reverse side of the coin shows the big apparel manufacturing running to the extremes to meet the production targets. The fast changing economic conditions such as global competition, declining profit margin, customer demand for high quality product, product variety, change of customer taste from seasons to seasons and reduced leadtime etc. had a major impact on the apparel manufacturing industries. The demand for higher value at lower price is increasing and to survive, apparel manufacturers need to improve their operations through producing right first time quality and waste reduction are the only tools of not only surviving in the market but also help in having a steady growth pace within the competitors.

The only point that speaks in favour of the manufacturer is the quality of the garment. The garment quality is inversely proportional to the no. of defects occurred during the manufacturing process. To have a control over the defects every manufacturing organization tried to implement a whole lot of things like 5s, six sigma, kanban principles, poka-yoke, traffic light system, kaizen principles, lean manufacturing process etc. but still defects happen during the manufacturing process.

The defects occurring in the manufacturing process can be classified under five major categories:-

Fabric Defects
Machine defects
v Broken Stitches

v Skip Stitches

v Uneven spi( stitch per inch)

v Puckering formation

v Loose tension

v Unsecure button/snaps

Skill/Human Made defects
v Uneven stitches

v Hi/Low stitches

v Raw edges

v Needle holes

v Pleat formations

v Missing operations

v Run off stitch

v Incorrect label attachment

Cleanliness Issues
v Dirt marks

v Oil stains

v Stickers present

v Gum stains

v Uncut threads

Out of tolerance
v Due to improper washing

v Due to improper ironing

The Problem Analysis & Findings: Uncut/loose threads are one of those defects which are casually passed by the checkers of sewing as well as finishing department. This on later stage causes pieces rejection of the style during the inspection process, thus not meeting the aql( acceptable quality limit) standard set by the buyer. The casualness of the operators and the checkers eats away the leadtime of the style thus increases the cost of production of the styles running in the organizations.

The operators in India have a very bad habit of continuous running of the machine thus forming an attachment between the ends of two pieces. When the desired operation is completed in all the pieces or there is a requirement of thread change in the machine the operator stops the machine and during this time he/she cuts the chain that has been formed between the pieces due to the sewing threads. The operator mainly doesnt trim the threads properly thus making a defect at the first step only, this practice is then continued by the other operators thus leading to a defective garment at the end of the line which is full of little uncut/loose threads. This mentality of the operators happens to developed just because they are always under the pressure to meet the hourly production target so that the WIP can be properly maintained. The probable areas in the garment where uncut/loose threads can be found are:-

Shirts/T-Shirts
v Buttons

v Button holes

v Bartacks

v Bottom hemming

v Collar area

v Armhole area

v Sleeves placket

v Front pocket

Trousers/Denims
v Waistband

v Waistband loops

v Buttons

v Buttonholes

v bartacks

v Carelabels

v Back pockets

v Crotch attachment

v Pocket bags

v Bottom hemming

v Fly attachment

Key ways to solve the problems: To maintain 100% quality many organizations have implemented many things but the proper training of the operators can only help them to achieve the mammoth target. Many organizations have also faced the scenario that all quality procedures are implemented in the organization but the implementation procedure is not properly percolated to the grass root level of the operators due to which the organization has suffered many setbacks. The proper enlightment of the operators with the procedures along with proper interval checkpoints can help to bud down the menace of loose/uncut threads.

The traffic light system is one of the best examples in controlling the problem because of its visual communication. At the same time it measure operators performance level in quality. This system is basically a combination of work between the line quality supervisors and the line operators. She/he has to check the semi finished garment pieces from current bundle once in an hour or two. Pieces will be taken randomly and check all the quality parameters required for that operation. The red card is given for those, who are identified by the line supervisor have produced 5 or more defective item out of ten pieces inspected. The yellow card is given to those who are identified by the line supervisor have produced 2 or more defective items out of ten inspected. The green card is given if no reworks are found. This system not only reduces the quality problems but it also increases the morale of the operators to achieve higher quality levels. Thus it will further reduce the cost and time of rework on the piece.

Dear friends,
Attention please. I've collected some soft copies of important books on Textile Engineering (Internatioal Version) from different sources.
How can I upload these books in our page? Please inform me if anyone of you know this. I already tried several times but I was failed. I think these books will be helpful for all of us. I can't find any option to upload & feeling helpless. I will appreciate any suggesion from anyone regarding this issue.
Thanks to all-------

Assignment on
“Dyestuff classification and dye selection”
Course title: Wet Processing Technology III
Course code: WPT 401

Submitted to:
Dr. AKM Saiful Islam
Head of the Department
Department of Textile Engineering
City University

Submitted by:
Md. Roman Khandakar
Department of Textile Engineering
ID 121297222
Batch: 2oth

Date of submission: 16/06/2015



Index

Topic Page No
1. Introduction of Dye & Dyes …………………………………………………………………..3
2. Etymology & History of Dyeing ……………………………………………………………….4
3 Dye classification according to origin…….……….…………….………………………… (4-7)
4. Dye classification according to application ……….………………………..…………….. (7-9)
5. Chemical classification of dyes …………………………………….……………….……….10
6. Selection of dyes or dyestuff…………………………………………………………… (10-11)
7. Factors to be considered for selecting dyestuff…………………………………………… (12)
8. Application of dyes……………………………………………………………………..… (12)
9 Conclusion ………………………………………………………………………..….…… (12)

Dye:
Dyeing is the process of adding color to textile products like fibers, yarns, and fabrics. Dyeing is normally done in a special solution containing dyes and particular chemical material. After dyeing, dye molecules have uncut chemical bond with fiber molecules. The temperature and time controlling are two key factors in dyeing. There are mainly two classes of dye, natural and manmade.
The primary source of dye, historically, has generally been nature, with the dyes being extracted from animals or plants. Since the mid-18th century, however, humans have produced artificial dyes to achieve a broader range of colors and to render the dyes more stable to resist 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 completed 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.

Dyes: Dyes are used for coloring the fabrics. Dyes are molecules which absorb and reflect light at specific wavelengths to give human eyes the sense of color. There are two major types of dyes - natural and synthetic dyes. The natural dyes are extracted from natural substances such as plants, animals, or minerals. Synthetic dyes are made in a laboratory.

Etymology:
The word dye is from Middle English deie and from Old English dag and dah. The first known use of the word dye was before the 12th century.
History of dyeing:
Archaeologists have found evidence of textile dyeing dating back to the Neolithic period. The earliest surviving evidence of textile dyeing was found 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. 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 Tyrian purple and kermes and plant-based dyes such as wood, 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. The development of new, strongly colored synthetic dyes followed quickly, and by the 1870s commercial dyeing with natural dyestuffs was disappearing.
Classification dyes according to origin:
1. Natural dyes:
The majority of natural dyes are from plant sources – roots, berries, bark, leaves, and wood, fungi, and lichens. Textile dyeing dates back to the Neolithic period. Throughout history, people have dyed their textiles using common, locally available materials. Scarce dyestuffs that produced brilliant and permanent colors such as the natural invertebrate dyes Tyrian purple and crimson kermes were highly prized luxury items in the ancient and medieval world. Plant-based dyes such as woad, indigo, saffron, and madder were raised commercially and were important trade goods in the economies of Asia and Europe. Across Asia and Africa, patterned fabrics were produced using resist dyeing techniques to control the absorption of color in piece-dyed cloth. Dyes from the New World such as cochineal and logwood were brought to Europe by the Spanish treasure fleets, and the dyestuffs of Europe were carried by colonists to America.
Dyed flax fibers have been found in the Republic of Georgia in a prehistoric cave dated to 36,000 BP. Archaeological evidence shows that, particularly in India and Phoenicia, dyeing has been widely carried out for over 5,000 years. The dyes were obtained from animal, vegetable or mineral origin, with none to very little processing. By far the greatest source of dyes has been from the plant kingdom, notably roots, berries, bark, leaves and wood, but only a few have ever been used on a commercial scale.
2. Synthetic dyes:
The first human-made organic aniline dye, mauveine, was discovered serendipitously by William Henry Perkin in 1856, the result of a failed attempt at the total synthesis of quinine. Other aniline dyes followed, such as fuchsine, safranine, and induline. Many thousands of synthetic dyes have since been prepared.
Synthetic dyes quickly replaced the traditional natural dyes. They cost less, they offered a vast range of new colors, and they imparted better properties to the dyed materials. Dyes are now classified according to the process used for their application to the fibers.

Natural dyes have been used since the beginning of organized society, developed so humans could paint their bodies, clothes, houses, weapons and religious icons. The colors were obtained from plants, animals, fruits and earth. In Mexico, they include indigo, cochineal (the bug parasite of the prickly pear cactus paddle), moss, nut shells and leaves, wild flowers, tree bark, and even a sea snail that emits a deep purple ink. Natural dyes are scarce, higher priced, and require a much longer, more complex process to produce.
For example, to make red using cochineal requires one day to grind the grain of the cochineal bug (cultivated on the cactus for three months), one day to prepare the wool, one day to mordant the wool, and one day to dye the wool. This does not factor in the three-to-six months of time required to “grow” the bug on the cactus. To produce a synthetic red dye takes one day. Color variation and intensity is controlled by adding more dye to the solution. It is not the complex chemistry that is involved in the natural dyeing process.
Intensity and Brilliance:
Natural dye color variation and brilliance is achieved by mixing different mordant with one batch of skeins, manipulating the PH of the dye baths, investing hours of time for one color. Colors obtained from natural sources tend to be earthy and subtle. Synthetic dyes often produce garish, stark or muddy colors. Wool rugs prepared with natural dyes are colorfast and will last a lifetime. Colorfastness can be tested by rubbing the surface of the weaving (if the weaver lets you) with a damp cloth. If the dye does not transfer, there is a good chance that the color is permanent.
The Price Difference:
Natural dye materials are scarce and expensive. For example, cochineal is more costly per ounce than gold. Synthetic dyes are readily available at low cost, resulting in a less costly rug to produce. Density of weave also adds to quality and therefore to cost. A low cost rug will likely be woven with synthetic dyes, on brittle; machine spun (not hand-spun) wool, and has a looser weave.

Health and Wellness:
The chemical fumes that are breathed in from the vapors of the dye pot are toxic. Sulfuric acid is potent and can burn the skin. If it splashes into the eye a person can go blind. Because people dye at home and there are not regulations around the use of chemical dyes, most people don’t take necessary precautions to use a face mask. As a result, over time many develop respiratory problems and lung cancer. A movement toward the use of natural dyes is also a good public health step. If you buy a rug dyed with natural materials, even though it may be more expensive, you know you are making a difference for a healthier life.
Natural dyes are far superior to chemical dyes for certain reasons:
- With exposure to light all color fades, but natural dyes fade or mellow leaving lighter tones that are just as beautiful, if not more so, than the original color.
- Natural dyes are more compatible and harmonious with one another. By contrast, chemical colors are easy to use and can produce good results, but have certain drawbacks, in that they can look hard or garish; some fade very quickly, and others fade uneven.

- One of the key reasons why natural colors look better than chemical colors because they are not 'pure' color: a natural red, for example, will include blue and yellow, whereas a chemical red will only contain red pigment. The impurities of natural dyes, which may comprise from five to 25 percent of the dye, consist of other hues that are similar to the main one, and it is these mixtures that make natural dyes so beautiful and create their harmony with neighboring natural colors. Where one person will see some purple in a hank of gray yarn, another may see some blue in it. To be able to see the difference is partly genetic, like the ability to curl one's tongue lengthwise, and partly a matter of experience. On the other hand, evenness of a synthetically dyed carpet is flat and uninteresting. Natural dye, precisely because of its unevenness, makes color vibrate or sparkle. And for some people this "imperfection," a sign of the artist's hand working natural substances from the garden or fields, has spiritual overtones.
- Natural dyes make different shades at the different time of the day. When these natural dyes expose to the light, they leave lighter tones, which makes them to look beautiful in different way than their original colors.
- Natural-dye enthusiasts see "mellow" hues that sparkle and glow which give esthetically comfortable feeling. But to be able to see these features one needs, perhaps, a passion for color.
- Natural dyes are substantially less destructive to the environment than the chemical dyes widely in use. Synthetic dyes used in textile dyeing generally cause environmental pollution and health problems in humans.
- Each plant provides an amazing diversity of shades. From one plant one may obtain between 5-15 varying colors and shades. These colors and shades are subtle and tend to harmonize with one another. The resulting fabrics or fibers are now original pieces - it is extremely difficult for anyone to duplicate exactly (even the dyer).
- Natural color is inherently more muted than chemical color, which looks very stark, and so if chemical colors are used while the desired effect is for the 'natural' look, it will be necessary to mix a variety of colors in imitation of nature.
- Color created from natural elements lasts much longer than chemical dyes.

Classification of dye according to application:
Reactive Dyes
Acid Dyes
Pre-metalized Dyes
Direct Dyes
Azoic Dyes
Disperse Dyes
Vat Dyes
Sulfur Dyes
Basic Dyes
Mordant Dyes
1. Reactive Dyes:Reactive dyes are the most recent of dyes. These are the most popular in the world among fiber and fabric artists, used at first only by surface designers, but recently by weavers as well. There are now reactive dyes for a wide range of fibers, e.g. cotton (PROCION), silk and wool (PROCILAN). The dye actually reacts with the fiber molecules to form color and is, as a result, extremely fast to both light and washing. There are hot and cold water reactive dyes, in fact there is a dye for almost every need. They can be most successfully used for silk painting, with a much better color fastness than the traditional basic dyes, and are already used by batik artists. We can identify a reactive dye by the alkali used to set off the fixation process, which requires time to take place (silk and wool reactive uses acetic acid). Assistants used are salt, soda ash and resist salt, and sometimes bicarbonate of soda and urea. Reactive dyes are equally suited to screen printing polychromatic printing, fabric painting yarn and piece dyeing. 2. Acid Dyes:Acid dyes are water-soluble anionic dyes that are applied to fibers such as silk, wool, nylon and modified acrylic fibers using neutral to acid dye baths. Attachment to the fiber is attributed, at least partly, to salt formation between anionic groups in the dyes and cationic groups in the fiber. Acid dyes are not substantive to cellulosic fibers. Most synthetic food colors fall in this category.
3. Pre-metalized Dyes:These are an acid dyes with the addition of one or two molecules of chromium. The dyes give mutetonings, not unlike those of natural dyes. They are the synthetic dyes mostly used by weavers who dye their own yarns. 4. Direct Dyes: 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) or sodium carbonate (Na2CO3). Direct dyes are used on cotton, paper, leather, wool, silk and nylon. They are also used as pH indicators and as biological stains.
5. Azoic (Napthol) Dyes: These are another sort of direct dye, but ones that are extremely fast to washing, bleach and light. They are intended for cellulose fibers and can be used successfully on protein fibers, although the colors are different. These dyes are widely used all over Asia and Australia for batik and direct application. They can be used to give interesting texture color effects on fabric, thread or paper. Their use for straight silk painting is minimal because of the difficulty in achieving evenness of painted color. Azoic dyeing is a technique in which an insoluble azo 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 azo dye. This technique of dyeing is unique, in that the final color is controlled by the choice of the diazoic and coupling components. This method of dyeing cotton is declining in importance due to the toxic nature of the chemicals used.
6. Disperse Dyes: Disperse dyes were originally developed for the dyeing of cellulose acetate, and are water-insoluble. The dyes are finely ground in the presence of a dispersing agent and sold as a paste, or spray-dried and sold as a powder. Their main use is to dye polyester but they can also be used to dye nylon, cellulose triacetate, and acrylic fibres. In some cases, a dyeing temperature of 130 °C (266 °F) 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.
7. Vat Dyes: 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. The color of denim is due to indigo, the original vat dye.
8. Sulfur Dyes:
Sulfur dyes are inexpensive dyes used to dye cotton with dark colors. Dyeing is effected by hearing the fabric in a solution of an organic compound, typically a nitrophenol derivative, and sulfide or polysulfide. The organic compound reacts with the sulfide source to form dark colors that adhere to the fabric. Sulfur Black 1, the largest selling dye by volume, does not have a well defined chemical structure. They are cheap, generally have good wash-fastness, and are easy to apply. Sulfur dyes are predominantly black, brown, and dark blue. Red sulfur dyes are unknown, although a pink or lighter scarlet color is available.

9. Basic Dyes:
Basic dyes are water-soluble cationic dyes that are mainly applied to acrylic fibers, 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 fiber. Basic dyes are also used in the coloration of paper. The colors are very bright, but not very fast to light, washing, perspiration. Fastness is improved if they are given an after-treatment or steaming, e.g. French Silk dyes are basic dyes and should be steamed to fix.
10. Mordant Dyes:
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 color 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. It is important to note that many mordants, particularly those in the heavy metal category, can be hazardous to health and extreme care must be taken in using them.
Food dyes:
One other class that describes the role of dyes, rather than their mode of use, is the food dye. Because food dyes are classed as food additives, they are manufactured to a higher standard than some industrial dyes. Food dyes can be direct, mordant and vat dyes, and their use is strictly controlled by legislation. Many are azo dyes, although anthraquinone and triphenylmethane compounds are used for colors such as green and blue. Some naturally-occurring dyes are also used.
Other important dyes:
A number of other classes have also been established, including:
Oxidation bases, for mainly hair and fur
Laser dyes: see, for example, rhodamine 6G and coumarin dyes.
Leather dyes, for leather
Fluorescent brighteners, for textile fibres and paper
Solvent dyes, for wood staining and producing colored lacquers, solvent inks, coloring oils, waxes.
Contrast dyes, injected for magnetic resonance imaging, are essentially the same as clothing dye except they are coupled to an agent that has strong paramagnetic properties.
Mayhem's dye, used in water cooling for looks, often rebranded RIT dye
Chemical classification:
By the nature of their chromophore, dyes are divided into
Category: Acridine dyes, derivates of acridine
Category: Anthraquinone dyes, derivates of anthraquinone
Arylmethane dyes
Category: Diarylmethane dyes, based on diphenyl methane
Category: Triarylmethane dyes, derivates of triphenylmethane
Category: Azo dyes, based on -N=N- azo structure
Diazonium dyes, based on diazonium salts
Nitro dyes, based on a -NO2 nitro functional group
Nitroso dyes, based on a -N=O nitroso functional group
Phthalocyanine dyes, derivatives of phthalocyanine
Quinone-imine dyes, derivatives of quinone
Category:Azin dyes
Category:Eurhodin dyes
Category:Safranin dyes, derivates of safranin
Indamins
Category: Indophenol dyes, derivates of indophenol
Category: Oxazin dyes, derivates of oxazin
Oxazone dyes, derivates of oxazone
Category: Thiazine dyes, derivatives of thiazine
Category: Thiazole dyes, derivatives of thiazole
Xanthene dyes, derived from xanthene
Fluorene dyes, derivatives of fluorene
Pyronin dyes
Category: Fluorone dyes, based on fluorone
Category: Rhodamine dyes, derivatives of rhodamine

Selection of dyes or dyestuffs:
With the enormous host of dyes available to today’s textile industry, the choices are significant. Aside from each coloring agent’s ability to impregnate fibres and fabrics with different color intensities, each has specific functional characteristics that may make it more suitable for one project than for another.
One of the most important decisions that must be made in dye selection is influenced by the products final use. Colorfastness, the degree to which the dye can withstand fading, is crucial in many cases. Washables, for example, must be colorfast so bleeding, the running of color, will not take place when the garment is laundered or used for swimming. Fading is another factor that must be considered, especially when exposed to sunlight, as in the case of active sportswear.
Fabrics that are improperly colored cause numerous problems for mills, manufacturers, retailers, and consumers. One wrong dyeing decision can generate displeasure for every part of the distribution cycle. The consumer returns the damaged product to the merchant, often causing a refund of the purchase price; the retailer, in turn, returns the product to the manufacturer, requesting credit for returned goods; the producer finally becomes embattled with the mill and requests and adjustment. An in-depth study of the various dye classes and their properties is appropriate for anyone wishing to enter the textile industry – and, for that matter, anyone interested in a career in any aspect of the fashion world. Some of the general classifications are offered to give an indication of their important characteristics to the apparel, accessories, and home furnishings industries.

Acid:
Excellent to achieve bright colors; not fast to washing, but able to withstand the chemicals used in dry cleaning

Chrome:
Excellent colorfastness to light and washing; however, the resulting colors are dull.

Basic:
Bright shades are easily achieved; generally colorfastness to washing and light. Fabrics colored with this dye are usually resistant to crocking; the color will not rub off from friction.

Direct:
Poor colorfastness to laundering as well as to light pe*******on; dry cleanable in most cases

Disperse:
Their potential for colorfastness varies according to the fibers being colored; colorfastness to crocking, perspiration, and dry cleaning is generally good.

Reactive:
Perfect for bright colors; good overall colorfastness, except to chlorine, which eliminates it as a useful agent in the dyeing of swimsuit fabrics

Napthol:
Bright colors; colorfastness to light varies, depending on the specific makeup of the dye; colorfast to washing

Vat:
Excellent colorfastness to sunlight, washing and perspiration

Factors to be considered for selecting dyestuff:
1. Nature of the shade
2. Nature of the material
3. Availability of the dyes
4. Fastness of the dyed material
5. Chemistry between dye & fiber

Application of Dyes:
There are different types of dyes for dyeing textile goods. These dyes have different nature in fiber. It depends on fiber characteristics. Application of dyes in different fibers is given below:

Name of DyesApplicationAcid dyeManmade fiber (Nylon),
Natural fiber (Silk, Wool)Direct DyeManmade fiber (Viscose),
Natural fiber (Cotton)Vat dyeManmade fiber (Viscose),
Natural fiber (Cotton, Silk, Wool)Disperse dyeNylon, Polyester, Acrylic, Tri-acetate, Di-acetateBasic dyeJute, AcrylicReactive dyeCotton, Wool, Silk, Viscose, NylonSulfur dyeCotton, ViscoseMordant dyeCotton, Wool, SilkPigmentCotton, Manmade fiberMineralCotton, Wool, SilkAzoic dyeCotton, ViscoseAniline BlackCottonRapid and Rapidson dyeCottonOnium dyeCotton, Jute
Conclusion:
From the above discussion it’s clear that different dyestuffs are compatible for different textile materials. In order to achieve a better dyeing performance it’s necessary to select suitable dyestuff for the respective textiles. Though now a day’s synthetic dyes are broadly used to fulfill our daily necessaries but we should keep in mind that it’s also harmful for our environment which the gift from nature. In this regard comparatively natural dyes are eco-friendly as well as better in individual performance. Before using dyestuff we should be conscious about our environment and the others related factors also.
THE END