What is anodising?

Anodising (also spelled anodizing) is an electrochemical process that produces a hard, protective oxide layer on aluminium. The workpiece is connected as the anode in an acid bath, where the surface oxidises into aluminium oxide. In Dutch and German, the process is also known as eloxeren or Eloxieren.

How does anodising work?

The process runs in stages:

1. Cleaning — degrease and pickle the aluminium surface
2. Anodising — immerse in a sulphuric acid bath, connect as anode; current forms an oxide layer of 5–25 µm
3. Colouring (optional) — the porous oxide can absorb a dye
4. Sealing — the pores are closed in hot water, making the layer corrosion-resistant

Unlike a coating, the layer grows into the metal — it is inseparable from the aluminium.

Applications

Anodising is widely used in:

• Aluminium frames — facade elements, windows and doors
• Facade panels — durable outdoor cladding
• Architectural profiles — fascia, edge trims
• Industrial components — hardware, balustrades, handrails
• Decorative applications — furniture, lighting, sanitary fittings

Benefits

• Corrosion resistant — protects for years against weather
• Wear resistant — harder than the underlying aluminium
• Colour fast — colour sits within the layer, doesn’t peel
• Low maintenance — only cleaning with water and soap
• Electrically insulating — the oxide layer does not conduct current

Colours

• Natural — silver-grey aluminium appearance
• Black, bronze, gold — popular in architecture
• Champagne, grey — modern facades
• RAL shades — limited via immersion dyes

Anodising vs. powder coating

In powder coating, a powder paint is sprayed and baked onto the surface. In anodising, the surface itself is transformed. Anodising is more durable and scratch-resistant; powder coating offers more colour choice.

Related terms

• Aluminium
• Galvanising
• Powder coating
• Surface treatment
• Facade cladding

Want to learn more about construction terms? Visit our knowledge base at fredsdiyplans.com.