Surface Treatments & Finishes
Why Apply a Surface Treatment or Finish?
Materials rarely leave the factory ready to sell. Surface treatments and finishes are applied for two reasons: to protect a material against damage such as corrosion, moisture, UV light and wear, and to improve its appearance through colour, texture and gloss. For this paper you need to know specific named finishes for each material category — metals, papers and boards, polymers, systems, textiles and timbers — and be able to justify why a particular finish suits a particular product.
Surface finishes serve two purposes: functional protection (against corrosion, moisture, UV damage and wear) and aesthetic enhancement (colour, texture and gloss).
Metals
Ferrous metals such as mild steel corrode quickly if left unprotected, so most metal finishes exist to stop oxygen and moisture reaching the surface. Paint is the simplest option, sealing the surface and adding colour, but it can chip and expose the metal underneath. Electroplating uses an electric current to deposit a thin layer of a more corrosion-resistant metal, such as chromium or nickel, onto the surface — used on taps and bicycle parts for a bright, hard-wearing finish.
Dip coating: the heated component is dipped into a fluidised bed of polymer powder, which melts on contact to form a smooth, coloured, scratch-resistant coating. Used on wire dish racks and tool handles.
Powder coating: dry polymer powder is sprayed onto the metal using an electrostatic charge, then baked in an oven so it melts into a tough, even layer. It resists chipping better than paint and comes in a wide range of colours — used on bicycle frames, radiators and garden furniture.
Galvanising: the metal is coated in zinc, either by hot-dip galvanising (dipping in molten zinc) or electro-galvanising. Zinc acts as a sacrificial layer — it corrodes before the steel underneath does, even if the coating is scratched. Used on crash barriers, gates and roofing sheets.
Anodising thickens the natural oxide layer on aluminium using an electric current, making the surface harder and more resistant to corrosion. The porous surface readily absorbs dye, so anodised products can be produced in bright colours — used on window frames, kitchenware and phone casings.
Papers & Boards
Papers and boards mainly need finishes that add strength, shine or decoration rather than corrosion protection. Varnishing applies a thin, glossy, protective liquid coating that seals print and resists moisture and scuffing. Hot foil blocking presses a metallic or coloured foil onto the surface using a heated die, giving book covers and greetings cards a shiny, decorative detail. Embossing presses the material between shaped dies to raise or recess a pattern, adding a tactile quality without ink. Edge staining colours the cut edges of pages or board, often seen on premium notebooks and boxed sets.
Polymers
Polymers do not rust or rot, so their finishes are mostly aesthetic or add specific surface properties. Polishing buffs the surface with fine abrasives to create a high-gloss, transparent finish, commonly used on acrylic. Mouldings can also be produced using textured or fine-surface moulds, transferring a pattern or sheen directly during manufacture and avoiding a separate finishing step. Laser engraving uses a focused laser beam to burn a permanent design or text into the surface, commonly used for branding on plastic casings. Vinyl stickers are self-adhesive graphics applied after manufacture, while GRP pigments are mixed into glass-reinforced polyester resin before moulding, so the colour runs through the whole component rather than sitting on the surface.
Systems
Electronic products need finishes that protect components and identify parts, as much as finishes that look attractive. Metal plating on connectors and pins improves conductivity and resists corrosion at electrical contacts. Insulating coatings and coverings protect users from electric shock and protect circuits from dust and moisture. Resistor colour-code bands are a functional finish too — the printed bands identify a resistor's value and tolerance at a glance. Cases and enclosures are finished using the same processes as other metal or polymer products, including anodising, painting and screen printing for branding.
Textiles
Batik is a resist-dyeing technique: melted wax is applied to parts of the fabric to block dye from reaching them, and the wax is removed after dyeing to reveal a patterned design. Embroidery stitches coloured thread into the fabric surface to create decorative patterns, logos or text — used on school uniforms and branded clothing. Fabric painting applies colour directly to the surface with a brush or sponge, while resist dyeing more broadly covers techniques (including batik and tie-dye) that block dye from certain areas. Chemical finishes such as stain resist and fireproofing change the fabric's performance rather than its appearance.
You should be able to name at least one specific finish per material category and explain both its protective and aesthetic benefits, linked to a real product.
Timbers
Timber needs protecting from moisture, insects and UV light, or it will rot, warp or fade. Staining colours the wood while letting the grain show through, changing appearance without hiding the surface. Waxing and oiling both nourish and seal the surface with a natural sheen, and need reapplying periodically as they wear away — common on kitchen worktops and furniture. Varnishing provides a harder, more durable clear or tinted coating, and shellac is a traditional natural resin finish that dries quickly to a glossy shine, often used on musical instruments and antique furniture restoration.
The right finish depends on the product's environment, cost and purpose. Outdoor products need finishes with UV and weather resistance, such as galvanising or exterior varnish. Products that touch food need non-toxic, food-safe coatings. High-traffic surfaces, like tabletops or door handles, need finishes that resist scratching and wear. Always link your answer to the specific product and its conditions of use, not just to the material.