Fixing, Washing, and Finishing Processes
What the exam tests
Fixing, washing, and finishing questions cover fastness, steam or cure conditions, soaping, rinsing, drying, and the final handle of the cloth. Expect cause-and-effect questions linking process to colour fastness.
Core rules
- Reactive dyes usually need alkalinity, time, and heat; fixation may be by steaming, curing, or a cold pad-batch method depending on the system.
- Steaming provides moisture and heat; under-steaming leaves unfixed dye that bleeds in washing.
- Pigments need a binder cured at the binder supplier's temperature; under-cure gives poor rub fastness.
- Vat dyes require reduction, development, and oxidation; soaping after oxidation improves shade and fastness.
- Washing removes unfixed dye, thickener, and chemicals; start cool and build gradually to avoid shock and back-staining.
- Soaping improves crock fastness and colour brightness for many dyes; rinse to neutral.
- Finishing may include stretching, calendering, or softening; check that finishing does not mask poor fixation.
Worked example
A reactive-printed cotton bleeds heavily in the first wash. The workshop steamed for only a few minutes at low temperature. Reasoning: reactive dye has not diffused and bonded to the cellulose; longer, moist steaming at the specified condition is needed, followed by proper soaping and rinsing.
Traps
Do not wash immediately after printing without fixation. Do not use hard water or excessive detergent. Do not assume a darker shade means better fixation.