Finishing techniques and surface treatments
Design & Technology · GCSE · The School
A finish does more than one job at once
A finish protects a material. It might guard against moisture, rust or UV damage. A finish can also improve looks, through colour or shine. And it can add a function, like a non-slip or heat-resistant coating. One finish often does two or three of these jobs at once. So the "right" finish depends on which job matters most for that product.
Wood: varnish, paint and preservative
Varnish forms a clear, hard layer. It still shows the grain underneath, so it is chosen when looks matter. Paint fully covers the surface in colour, hiding the grain. It is often cheaper, and lasts well outdoors. Preservative soaks into the wood itself. It fights rot and insects, without changing how the wood looks very much.
Metal: galvanising, anodising and painting
Galvanising coats steel in a layer of zinc. The zinc corrodes instead of the steel underneath. It is used on outdoor things like fences and gutters. Anodising thickens the natural oxide layer on aluminium. This makes it harder, and lets it be dyed a colour — used on water bottles and bike frames. Painting metal works like painting wood: it protects and adds colour, but needs a primer first to stick properly.
A worked choice: an outdoor steel gate
An outdoor steel gate must resist rust for years, with little upkeep. Paint alone is not enough here. Its coating chips over time, and rust starts underneath. Galvanising is chosen instead. Its zinc layer corrodes first, protecting the steel even where the coating gets scratched. That is exactly what paint alone cannot do.
Polymers usually need little or no finish at all
Many polymers are coloured all the way through, during manufacture. This is called self-finished. There is no separate surface layer to wear off. So no different colour is revealed underneath if it gets scratched. Texture or printing on a polymer product is usually built in during moulding. It is rarely a separate step applied afterwards.
Choosing a finish means naming the reason, not just the name
Just naming "varnish" or "galvanising" is not enough for a full answer. State the material first. Then name the main risk it faces: rust, UV, or wear. Then explain how the chosen finish deals with THAT risk specifically. Those three parts, together, are what separate one finish choice from another in a real design decision.