For my sins, the wheels on the family Merc have not been cleaned other than by pressure washer for 5 years at least. The result has been an accumulation of black grime over a yellow stain.

Cleaned the car yesterday and decided to have a go at the alloy wheels using the technique I use for the yellow stain that accumulates round the water line of the boat. For this I mix up a slurry of oxalic acid and wall paper paste - the latter being there just to stop run off.

It worked like a dream leaving me with shiny silver wheels. Good rinse off to get rid of the remains of the acid and then a layer of polish.

Oxalic acid is poisonous but it isnt really nasty stuff like battery acid. Use commonsense and disposeable gloves in handling it. Its often an ingredient in teak cleaner.