Why is a finish almost never just about looks, and how do you pick the right one for the material and the job?
Why finishes are applied to materials for aesthetic, protective and functional reasons, and the finishing techniques used on metals (painting, anodising, powder coating, galvanising, electroplating), polymers, timbers (lacquering, varnishing, oils, waxes, staining) and textiles (dyeing, printing, chemical finishes).
A focused answer to AQA A-Level Design and Technology Product Design 3.1.5, covering why finishes are applied for aesthetic, protective and functional reasons and the main finishing techniques for metals, polymers, timbers and textiles.
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What this dot point is asking
AQA wants you to explain why a finish is applied (it is rarely only cosmetic) and to know the main finishing techniques for each material family, matching the finish to the material and to what the product must do.
Why finishes are applied
The three reasons overlap, and a good answer names which ones the product needs:
- Aesthetic: colour, gloss or matt texture and a quality feel that make the product attractive and saleable.
- Protective: keeping out moisture, UV light, corrosion and abrasion so the product lasts. This is why exterior products almost always need a finish.
- Functional: improving hygiene (a smooth wipe-clean surface), electrical insulation, chemical resistance or grip.
Finishing metals
Metals corrode, so most metal products are finished:
- Painting is cheap and gives any colour, but chips and needs maintenance.
- Anodising thickens the natural oxide layer on aluminium by electrolysis, giving a hard, corrosion-resistant surface that can be dyed and will not chip because it is part of the metal.
- Powder coating sprays a charged dry polymer powder that is baked into a tough, even, coloured film, common on bike frames and garden furniture.
- Galvanising dips steel in molten zinc to give a sacrificial coating that protects even when scratched, ideal for outdoor steel.
- Electroplating deposits a thin layer of another metal (chromium, nickel) for appearance and protection, as on taps and cutlery.
Finishing polymers
Many polymers are self-coloured during moulding (pigment added as an admixture), so they may need no finish at all, which is one of their advantages over metals and timber. Where a finish is wanted, polymers can be painted, printed (logos, graphics) or given a textured tool surface for grip. Some are coated or have a film or foil applied. Because polymers do not corrode, the reason for finishing them is usually aesthetic or for branding rather than protection.
Finishing timbers
Timber must be sealed against moisture, which would otherwise cause it to swell, rot or distort:
- Lacquering and varnishing lay a hard, clear film on the surface that resists moisture and wear while showing the grain.
- Oils (such as Danish or linseed) soak in to give a natural, low-sheen, water-resistant finish that is easy to repair.
- Waxes give a soft sheen but little protection, often over another finish.
- Stains and dyes change the colour while keeping the grain visible.
- Paint hides the grain and gives a coloured, protected surface, used where appearance, not the wood itself, matters.
The choice depends on whether the timber is for interior or exterior use and whether the grain should show.
Finishing textiles
Textiles are finished to change both look and performance:
- Dyeing colours the whole fabric or yarn.
- Printing applies a pattern to the surface.
- Chemical finishes add performance: flame-retardant (furnishings), water-repellent (outerwear), crease-resistant and stain-resistant treatments.
Exam-style practice questions
Practice questions written in the style of AQA exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
AQA 20186 marksA garden gate is to be made from steel. Discuss the finishing options available and recommend a finish, justifying your choice in terms of protection, aesthetics and cost. [6 marks]Show worked answer →
A Paper 1 extended item assessing AO3. Markers reward finishes linked to the exterior application, not a list. Award marks for naming and explaining relevant options: galvanising dips the steel in molten zinc to give a sacrificial coating that resists corrosion for decades even if scratched, but its grey spangled look is industrial; powder coating sprays a charged dry polymer powder that is then baked to a tough, even, coloured film, giving both protection and a wide colour choice; painting is cheapest but chips and needs repainting. Award marks for a justified recommendation: for a gate that lives outdoors, a galvanise-then-powder-coat (duplex) system gives the best durability and a chosen colour, with the higher cost justified by a long maintenance-free life. A top answer weighs protection against cost and notes that bare or merely painted steel would soon rust.
AQA 20214 marksExplain the difference between anodising and electroplating, and give one product suited to each. [4 marks]Show worked answer →
A short-answer item. Award marks for: anodising uses electrolysis to thicken the natural oxide layer on aluminium, giving a hard, corrosion-resistant surface that can be dyed a colour and is part of the metal itself, so it does not chip (example: a coloured aluminium drinks bottle or laptop case); electroplating uses electrolysis to deposit a thin layer of a different metal (such as chromium or nickel) onto the surface of another metal for protection or appearance, which can wear or flake over time (example: chrome-plated taps or steel cutlery). Full marks need the thicken-own-oxide versus deposit-another-metal distinction plus a valid example each. Confusing the two is the common error.
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