Design & Technology
Fabrics usually need to be washed, bleached and dyed before they are made into textile products. Garments are assembled using various joining techniques including sewing, fusing and heat-sealing. Finishing improves the appearance, handle and performance of fabrics, while pressing is used to shape and stabilise fabrics.
Before dyeing and printing the fabric is prepared by washing, bleaching and mercerising, in which the yarn is treated to improve strength, lustre and receptivity to dye. Fabrics can be dyed by hand or by machine.
In hand dyeing, fabrics are immersed in hot or cold dyes in a dye bath. The dye bath is agitated so the dye reaches all areas. When the desired colour is achieved the fabric is removed and rinsed to remove excess dye. Then it is fixed with a mordant or a fixing agent such as salt. The strength of a dye colour is determined by the:
In industrial production fabric is dyed by continuous or batch dyeing.
The fabric is passed through a dye bath, and then squeezed between rollers to spread the dye evenly and remove excess. Continuous dyeing is used for colours that do not need to change too quickly with fashion.
Fabrics are produced without dye. Instead, they are dyed to order in large batches according to the colours required. Batch dyeing is used for fabrics that have to change in colour frequently because of fashion.