Metals (Junior Cert Wood Technology): Revision Notes

Metal Finishes

When working on woodwork projects, you'll often encounter metals in the form of hinges, screws, handles, brackets, tools, and decorative elements. However, metals have a significant weakness - they're susceptible to corrosion. This means iron and steel can rust, while copper, brass, and silver can tarnish over time. Applying the right metal finish acts as a protective barrier that shields the surface, extends the component's lifespan, and enhances its visual appeal.

Why we need metal finishes

Metal finishes serve several crucial purposes that make them essential in both functional and decorative applications:

Protection - The primary benefit is preventing rust and tarnish, which significantly extends the life of metal components. Without proper finishing, expensive metal parts can deteriorate quickly when exposed to moisture and air.

Enhanced appearance - Finishes can transform the look of metal surfaces, providing bright polished effects, vibrant colours, or attractive shiny surfaces that complement your project's design.

Improved durability - Quality finishes help metal parts withstand daily wear and exposure to weather conditions, making them last much longer.

Safety considerations - Finishing removes rough edges and sharp surfaces that could cause injury during handling or use.

Easier maintenance - Finished surfaces are typically much easier to clean and keep in good condition compared to raw metal.

Common metal finishing techniques

Painting

This is perhaps the most widely recognised metal finishing method. The process begins with thoroughly cleaning the metal to remove any grease, dirt, or existing rust. Next, you apply a primer, which is a special undercoat designed specifically for metals that helps the final paint adhere properly. Finally, you apply oil-based or enamel paint for the topcoat.

The main advantage of painting is the vast range of colours available, plus it provides excellent protection against corrosion. However, painted surfaces can chip or scratch with heavy use, and they require regular maintenance to keep them looking good. You'll commonly see painted finishes on steel brackets, screws, and furniture fittings.

Lacquering

This technique involves first polishing the metal surface to achieve a brilliant shine, then applying a clear lacquer either by spraying or brushing. The lacquer acts as a transparent protective layer.

Lacquering is excellent for preserving the natural shiny appearance of metals whilst preventing tarnish, and it's relatively straightforward to apply. The downside is that the protective layer can gradually wear away over time and isn't as robust as paint. You'll often see lacquered finishes on brass handles, aluminium trims, and decorative screws.

Electroplating

This is a fascinating process that uses electrical current to deposit a thin layer of one metal onto the surface of another. For example, you might electroplate chromium onto steel or nickel onto brass.

The advantages include creating an attractive finish, adding corrosion resistance, and making inexpensive metals appear like costly ones. However, electroplating requires specialist equipment and the coating can wear away if the surface gets scratched. Chrome-plated taps, cutlery, and bicycle parts are common examples.

Galvanising

This process involves dipping iron or steel components into molten zinc, which creates a protective zinc coating on the surface.

Galvanising provides extremely strong protection against rust because zinc actually corrodes before the steel underneath, sacrificing itself to protect the base metal. The coating continues to protect even if scratched. The main drawback is the dull grey appearance unless painted over. You'll find galvanised finishes on outdoor nails, garden gates, hinges, and farm equipment.

Bluing (gun bluing)

This technique treats steel with heat or chemicals to create a thin, dark oxide coating on the surface.

Bluing produces an attractive black or blue appearance and offers some protection against rust. However, it only provides surface-level protection and is often combined with oiling for better results. This finish is commonly seen on tools, screws, and firearm components.

Powder coating

This modern technique involves spraying dry powder onto the metal using an electrostatic gun, then baking the coated item in an oven to form a hard finish.

Powder coating is exceptionally durable, offers a wide range of colours, and is highly scratch-resistant. The disadvantages are that it requires specialist equipment and isn't easy to repair if damaged. You'll see powder coating on school furniture frames, tool casings, and bicycle frames.

Polishing

This is the simplest finishing method, involving buffing the surface with abrasive wheels or paste until it achieves a bright shine.

Polishing creates an attractive bright surface and is a straightforward process. However, it provides minimal corrosion protection unless combined with lacquering. Brass ornaments and stainless steel fittings often use this finish.

Quick reference guide

Finish	How it works	Key advantages	Typical examples
Painting	Primer plus enamel/oil paint	Wide colour choice, strong protection	Brackets, screws
Lacquering	Clear coating over polished metal	Preserves shine, prevents tarnish	Brass handles, trims
Electroplating	Thin metal coating using electricity	Attractive appearance, corrosion resistant	Chrome taps, cutlery
Galvanising	Zinc coating by dipping in molten zinc	Excellent rust protection	Outdoor nails, gates
Bluing	Chemical/heat treatment creating oxide layer	Dark decorative colour, minor protection	Tools, screws
Powder coating	Electrostatic powder baked onto surface	Very tough, colourful, scratch-resistant	Furniture, bike frames
Polishing	Abrasive buffing until shiny	Attractive surface, simple process	Ornaments, fittings