This is the treatment of cotton or linen yarn or fabric with concentrated caustic alkali. It has the effect of swelling the fibres, increasing their strength and dye affinity and altering the luster and handle of the material. Mercerisers are either chain or chainless and consist of three sections, impregnation, stabilisation and washing off.

Most mercerisation units have their own caustic recovery systems to help minimise waste.

Principal pollutants: Alkaline effluent from washing and rinsing operations.

Effluent from mercerising operations consists mainly of mildy caustic rinse water. Typically the pH of this effluent is about 10 to 12. Water usage for this process is about 20 liters per kg of cloth.

The fabric, yarn or loose stock is now ready to receive colour. Dyestuffs can be applied by many different techniques to give shades that are fast to washing and light. Dyeing can be carried out at almost every stage of manufacture. Yarn dyeing is quite common, to obtain coloured yarns with which the weaver can produce a wide range of coloured striped or check designs for such fabrics as shirting, bedding and dress materials.