Introduction to Finishes and Preservation
Welcome! In this chapter, we are looking at the final "magic touch" of product design. Why do we bother finishing a product? Imagine a beautiful wooden garden bench left out in the rain without any protection—it wouldn't stay beautiful for long! Finishing and preservation are essential because they do two main jobs: they make a product look great (aesthetics) and they protect it from falling apart (preventing degradation).
Whether it’s preventing a steel gate from rusting or making a luxury chocolate box look shiny, understanding how to select the right finish is a vital skill for any designer. Let’s dive in!
1. Understanding Degradation: Why do things go wrong?
Before we can protect a material, we need to know what we are protecting it from. Degradation is the process where a material’s properties get worse over time due to its environment. Here are the main culprits:
Moisture and Oxygen: This is the "deadly duo" for metals like mild steel, leading to corrosion (rust). It also causes wood to rot or warp.
UV Light: Sunlight can bleach the colour out of polymers and woods, and even make some plastics brittle so they crack easily.
Chemicals and Pollution: Acids in rain or oils from human skin can eat away at surfaces.
Insects and Fungus: These are particularly fond of "eating" untreated timber.
Quick Tip: If a question asks why a specific finish is needed, always think about where the product will be used. A kitchen spatula needs to resist heat and water, while a car bumper needs to resist salt, rain, and UV light.
2. Metal Finishes and Protection
Metals are tough, but they are very prone to corrosion. We use several clever techniques to keep them in top condition.
Anodising
Used mainly for aluminium. This process uses an electric current to increase the thickness of the natural oxide layer on the metal's surface.
Why use it? It makes the surface harder and more resistant to scratches. It also allows us to add vibrant dyes, which is why you see colourful aluminium water bottles or electronics.
Electro-plating
This involves using electricity to coat a cheap base metal (like steel) with a thin layer of a more expensive or protective metal (like silver, gold, or chrome).
Why use it? To make a product look expensive or to provide a hard, shiny, corrosion-resistant surface (like a chrome-plated tap).
Powder Coating
The product is given a negative static charge, and a dry powder (paint) is given a positive charge. The powder is sprayed on and sticks perfectly because of the static electricity. It is then baked in an oven to melt the powder into a hard skin.
Why use it? It is much tougher than liquid paint and is very common on washing machines, bicycle frames, and metal furniture.
Galvanisation
This is the process of dipping steel into a bath of molten zinc.
Why use it? The zinc acts as a "sacrificial" layer. Even if the coating is scratched, the zinc will corrode instead of the steel. You’ll see this on lamp posts, industrial gates, and buckets.
Cathodic Protection
This is a high-level protection method for large steel structures like underground pipelines or boat hulls. It works by making the metal structure the "cathode" of an electrochemical cell. We attach a "sacrificial anode" (a block of more reactive metal like magnesium or zinc) to the structure. The anode corrodes away, saving the main structure.
Key Takeaway: It’s like a bodyguard taking the "hit" so the main product stays safe.
Oil Coating and Painting
Oil coating is a simple way to protect tools or engine parts; it creates a slippery barrier that keeps moisture off the metal. Paints for metal are specialized barriers that seal the surface away from the air.
3. Wood Finishes and General Preservation
Wood is "organic," which means it wants to break down. We use these finishes to stop that process.
Paints: These provide a solid colour and a thick protective barrier. Great for low-quality woods to hide the grain.
Varnishes: These are clear coatings (polyurethane is common) that protect the wood but let the natural beauty of the grain show through. They can be gloss, matt, or satin.
Sealants: These are applied to block the pores of the wood, stopping it from absorbing water or "bleeding" sap. They are often used under a final coat of paint.
Preservatives: These are chemicals soaked into the wood (often under pressure) to kill insects and prevent fungus or rot. Essential for fences, decking, and sheds.
4. Paper and Board Finishing
In the world of commercial printing and packaging (think of a high-end perfume box), finishes make the product feel "premium."
Laminating
A thin layer of plastic (usually PP or PET) is bonded to the surface of the paper or board using heat and pressure.
Why use it? It makes the paper wipe-clean, much stronger, and tear-resistant. Think of a restaurant menu.
Varnishing (Paper)
A clear ink is applied to the surface. It can be applied to the whole page or just certain spots (called Spot UV) to make them shine.
Why use it? It creates a high-quality feel and protects the print from smudging.
Hot Foil Blocking
A heated metal die (stamp) is used to press a thin metallic foil onto the paper.
Why use it? It creates a shiny, metallic finish (usually gold or silver) that you can't achieve with normal printing. It is used on luxury packaging and greeting cards.
Embossing
This uses two metal dies to "squish" the paper, raising the surface to create a 3D texture.
Why use it? It adds a tactile (touch) element to the design. It feels fancy and high-quality because you can feel the shape with your fingers.
Quick Review: Choosing the Right Finish
When you are deciding on a finish in your exam or your NEA (Non-Examined Assessment), ask yourself these three questions:
1. Environment: Will it be outside? (Needs weatherproofing like galvanisation or preservatives).
2. Usage: Will it be handled a lot? (Needs a hard-wearing finish like powder coating or laminating).
3. Cost: Is it a luxury item? (Can afford hot foil blocking or electro-plating).
4. Safety: If it's a child's toy, is the finish non-toxic? (Check the paint type).
Common Mistake to Avoid: Don't just say "paint it." Be specific! Is it polyurethane varnish for a table? Is it powder coating for a metal chair? Being specific gets you the marks.
Key Takeaway Summary:
- Metal: Protects against corrosion (rust) using barriers (paint/oil) or sacrificial layers (galvanisation/cathodic protection).
- Wood: Protects against rot and insects using preservatives and seals the surface with varnish.
- Paper/Board: Enhances the "unboxing" experience through textures (embossing) and shine (foil/varnish).