Explain scouring and bleaching.

1. 1 · Open in two lines. Scouring and bleaching are general (preparatory) finishes. Scouring cleans the cloth; bleaching whitens it.
2. 2 · Draw the flow chart. [Flow chart: grey cloth → singeing → desizing → scouring → bleaching → mercerizing → dyeing or printing → final finishes]
3. 3 · Aim of scouring. Remove natural impurities (wax, pectin, grease, gum) and added ones (oil, size, dirt) to make cloth clean and absorbent.
4. 4 · Scouring each fibre.
   • Cotton: kier boiling with caustic soda.
   • Wool: warm soap and soda ash, little agitation.
   • Silk: degumming in soap solution.
   • Synthetics: light detergent scour.
5. 5 · Bleaching agents.
   • Oxidising: hydrogen peroxide (all), hypochlorite (cotton, linen), chlorite (synthetics), perborate (detergents).
   • Reducing: hydrosulphite, sulphur dioxide (wool, silk).
   • Optical brighteners: look whiter, not a bleach.
6. 6 · Precautions. Match the bleach to the fibre, control strength and temperature, rinse and neutralise, and check strength afterwards.
7. 7 · Daily-life link. Chlorine bleach only for white cotton hospital and kitchen linen; peroxide for delicate and coloured clothes.
8. 8 · Close in one line. Clean, absorbent, white cloth from scouring and bleaching is the base for every later finish.

Scoring tip: A table of bleaches with 'suits' and 'harms' columns is quick to write and examiners look for it.