Anodising aluminium

What's it all about?

Anodising is a process that increases the thickness of the natural aluminium oxide layer on the surface of aluminium. It is called anodising because the aluminium is made the anode (positive electrode) in an electric circuit.

Aluminium can be anodised fairly easily, and then dyed permanently using fabric dyes or fountain pen ink. Used soft drinks cans are an inexpensive source of aluminium sheet, but you could buy new sheet instead. Anodising can be used to produce home-made jewellery and badges.

Student notes

There are four parts to this activity:

Preparing the aluminium

Using the scissors, cut out a piece of aluminium from your can. Watch out for sharp edges! About 5 cm × 2 cm is okay. Make a hole in the strip at one end. Bend one end of a length of copper wire to make a hook, and put it through the hole. From now on, only hold the aluminium using the wire – not your sticky paws!

Fill a large beaker about ¾ full with distilled water (not tap water). Take your beaker and the piece of aluminium to the fume cupboard. Ask one of the teachers to clean your aluminium for you. After cleaning, put it into your beaker of distilled water for you to carry back to your bench.

Preparing the anodising cell

Now you have to set up the anodising cell. Put the 500 cm3 beaker on top of some paper towels. Lay the glass rod on top of the beaker. Hang the piece of lead from the rod using the copper wire. The lead should hang just above the bottom of the beaker. Make sure that some copper wire sticks up from the rod. This will let you make an electrical connection.

Do the same thing with your cleaned aluminium strip, but don’t touch it with your hands and don’t let it touch the lead.


You are now ready to start anodising. For it to work, you must complete the electrical cell with sulfuric acid (this will conduct electricity between the lead and aluminium). Carefully pour dilute sulfuric acid into the beaker. You need just enough to cover most of the lead and most of the aluminium strip (but leave about 1 cm above the surface).

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Anodised and dyed metal parts


You are now ready to colour the aluminium strip. Try one colour first, because you can be more artistic with another strip later. To colour the strip, you just put into the dye of your choice. Leave the strip in the dye for 10 minutes, but move it about a bit every minute. After 10 minutes, remove your aluminium strip from the dye solution. Put it on a watch glass. Wash it under a running tap to get rid of excess dye. To seal your aluminium strip, put it in a beaker of boiled water from the kettle for 10 minutes. The dye is now permanently sealed into the aluminium oxide layer.

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Teacher Guide

Activity notes

There are several methods for simple anodising of aluminium. We use a lead cathode with a copper wire already soldered on, but you can use a large piece of aluminium instead. Preparation and patience is important – if students rush the cleaning and anodising stages, they get a poor result. We find that many drinks cans have a thin plastic coating on the inside. This can be removed using wire wool, or left in place if only one side is to be dyed.

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Health and Safety

When considering carrying out a practical activity with a class, you must check your local health and safety rules. Make an appropriate risk assessment and try the activity yourself first.

Technician notes

Per group of students:

  • 2 × 250 cm3 plastic beakers
  • 1 × glass rod
  • 1 × watch glass
  • 1 × power pack
  • 2 × 10 cm lengths of copper wire
  • 2 × electrical leads with crocodile clips
  • 1 × lead sheet, approx. 2 cm × 5 cm [or aluminium sheet]
  • aluminium drinks cans (washed)
  • fine steel wool
  • paper towels
  • wash bottle containing distilled water
  • 250 cm3 bottle of 1 M sulfuric acid, labelled “1 M sulfuric acid – Irritant”
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aluminium sheet
Beware of sharp edges and corners.

lead metal
Harmful if swallowed or inhaled. Wear gloves and avoid raising a dust. May be of concern to pregnant women.

1 M sulfuric acid
Irritating to the skin and eyes. Avoid skin contact and wear eye protection.

3 M nitric acid
Corrosive. Wear chemical-resistant gloves and splash-proof goggles.

1.5 M sodium hydroxide solution
Corrosive. Wear chemical-resistant gloves and splash-proof goggles.