Finishing

"Sand it" loses the technique marks. Glasspaper must be worked along the grain, not across it -- across drags the fibres and leaves scratches visible under a clear finish. Work through progressively finer grades, and wrap the paper round a cork rubber (sanding block) so it presses evenly. Name the along-the-grain direction, the finer sequence and the cork rubber.

For a mirror edge on acrylic, filing and draw-filing come first to remove saw marks, then the surface is rubbed with wet-and-dry (silicon-carbide) paper used wet through finer grades, and finally buffed with a polishing mop and compound. Jumping straight to a mop, or stopping at filing, misses the wet-and-dry and buffing stages that produce the mirror finish.

Dip-coating is poorly described. The stages: clean and heat the metal in an oven (around 180 C) so powder melts on it; dip it into a fluidised bed -- polyethylene powder kept floating by air blown up through it; the hot metal melts the powder onto it; return it briefly to the oven to flow smooth; then cool. Common gaps: forgetting the pre-heat, or thinking the part is sprayed.

When a question says other than PPE, writing wear goggles or gloves scores zero -- those are excluded. Give process-specific precautions: work in a well-ventilated area because paint and solvent fumes are harmful; keep solvent finishes away from naked flames because they are flammable; dispose of solvent-soaked rags safely. Answer about the process, not what you wear.

A common wrong belief is that staining wood both colours and protects it. A stain soaks in to change the colour while letting the grain show, but it forms no protective film and barely resists moisture or wear, so stained wood still absorbs water and marks easily. To protect it, apply a clear topcoat over the stain -- varnish, lacquer or oil. Stain colours, topcoat protects.

Candidates muddle the three layers of a paint system or skip one. The primer goes on first -- it seals and keys to the bare surface and, on metal, inhibits rust. The undercoat builds the film and evens the base for the colour. The topcoat gives the colour, sheen and the weather- and wear-resistant outer skin. Missing the primer is why paint flakes or rust creeps through.

A confusion: that anodising equals electroplating, or that anodising coats aluminium with another metal. It does not. Anodising passes a current through aluminium to thicken its own oxide -- no new metal is added; the harder, porous oxide resists corrosion and can be dyed, and the object is the anode. Electroplating adds a different metal, and there the object is the cathode.