Dyeing and finishing: the process line
Cloth straight from the loom is called grey cloth (greige). It has oil, dirt and size (starch) on it. It is turned into a product in wet processing steps:
- Preparation. Desizing (remove starch), scouring (remove oil and wax) and bleaching (make it white). Without this, dye goes on unevenly.
- Dyeing or printing. Adds colour.
- Finishing. Gives the final feel and performance.
Colour can be added at four stages: fibre (stock) dyeing, yarn dyeing (for stripes and checks), piece (fabric) dyeing (most common) and garment dyeing (colour chosen late, so less waste).
Dyeing machines include the jig (cloth rolls from one roller to another through the bath), the winch, the jet (cloth circulates in a fast stream of dye liquor) and the pad-batch (cloth is squeezed through a dye tray, then rolled and left to react).
Dyeing and printing compared
Dyeing colours the whole cloth with a uniform colour. Printing applies colour as a pattern, using a thick paste of dye or pigment. Methods: roller printing (engraved copper rollers), screen printing (paste pushed through a mesh with open pattern areas), block printing (hand-carved wooden blocks, popular in India), and digital printing (an inkjet prints the pattern straight from a computer file). After printing, the colour is fixed with steam or heat and washed.
Finish machining
Mechanical finishes use machines, heat and pressure, not chemicals, to change the cloth.
- Calendering: cloth passes between heavy hot rollers. It becomes smooth, flat and shiny.
- Raising (napping): wire or teasel brushes lift tiny fibre ends. The cloth becomes fuzzy and warm (flannel, fleece).
- Shearing: blades cut the raised fibres to an even length for a smooth, even surface.
- Heat setting: heating synthetic cloth under tension so it holds its shape and does not shrink or wrinkle later.
- Sanforising: cloth is squeezed so that it shrinks before it is sold, so your shirt does not shrink in the wash.
- Stentering: cloth is stretched to the right width and dried.
Surface processing and treatment
Surface treatments add a new property to the cloth, mostly with chemicals or special coatings.
- Mercerising: cotton is treated with strong caustic soda under tension. The fibre swells, becomes round, shinier, stronger and takes dye better.
- Water-repellent finish: a coating makes water form beads and roll off, while air can still pass. (Waterproof coating blocks air too.)
- Flame-retardant finish: chemicals make cloth burn slowly or stop burning. Used for children's night clothes, curtains and uniforms.
- Anti-crease (easy-care) finish: a resin links the cotton chains so they spring back after folding.
- Coating and laminating: a layer of plastic or rubber is added, as in raincoats and tents.
- Plasma and enzyme treatment: modern, low-water ways to change the surface. For example, enzymes remove fuzz from cotton (bio-polishing).
Try it
In the 3D, use the picker and see the bars for each finish. At home: put a drop of water on a raincoat, a cotton shirt and a polyester shirt. Which one makes a bead? Which one soaks it in? Note it down, then explain why.
Key formulas and definitions
- Grey cloth → preparation → dyeing/printing → finish machining → surface treatment
- Stages of dyeing: fibre → yarn → fabric → garment
- Mechanical finish: calendering, raising, shearing, heat setting, sanforising
- Surface treatment: mercerising, water repellent, flame retardant, anti-crease
Worked examples
1. Why is cloth scoured and bleached before dyeing?
Scouring removes oil, wax and dirt; bleaching removes natural colour. A clean white base takes dye evenly, so the final colour has no patches.
2. Which dyeing stage would you choose for a striped shirt, and why?
Yarn dyeing. The yarns are dyed in different colours first and then woven, so the stripes or checks come from the weave.
3. A shirt maker wants a smooth, shiny cotton and a flannel that is soft and fuzzy. Name the finish for each.
Smooth and shiny: calendering (or mercerising). Soft and fuzzy: raising (napping).
4. What is the difference between a water-repellent and a waterproof fabric?
Water-repellent cloth makes water roll off in beads but lets air through, so it is breathable. A waterproof coated fabric blocks water and air.
5. Why is sanforising done on denim and cotton shirts?
The cloth is made to shrink in the factory, so after you wash it, it does not shrink more and the shirt keeps its size.
Common mistakes
- Thinking dyeing and printing are the same. Dyeing colours all of the cloth; printing puts colour only in a pattern.
- Mixing up water-repellent and waterproof.
- Believing every finish needs chemicals. Calendering, raising, shearing and heat setting are mechanical.
- Forgetting that grey cloth must be prepared (desized, scoured, bleached) before it can be dyed evenly.