Aluminium

Most aluminium objects found in museum collections will be alloys containing copper as a minor component. The addition of only 3 % (by weight) of copper trebles the mechanical strength of the parent metal.

As aluminium corrodes the oxide layer that forms protects the surface against further corrosion. Under normal environmental conditions the metal does not corrode to any great extent.

Deterioration

If allowed to come into contact with metals such as copper and iron, or in the presence of chloride ions (such as found in sea water), aluminium and its alloys corrode appreciably.

Do not allow aluminium to come into contact with mercury as mercury prevents formation of the protective oxide patina, promoting rapid corrosion of the aluminium.

Preventive Conservation

Apply the guidelines described in the general introduction to this chapter to aluminium and its alloys.

Treatments

Cleaning

Clean aluminium with methylated spirits or a soft brush to remove dirt. Do not use any abrasives on aluminium as these may remove the protective oxide layer.

Never use caustic soda to remove grease or paint from aluminium objects as it reacts vigorously with aluminium. Remove heavy deposits of oil, grease and petroleum products, commonly encountered on vintage car parts, with kerosene or similar products.

If the metal is heavily stained or corroded, apply a solution of phosphoric acid (1 %). This will produce a mild uniform etch on the metal surface which, after thorough washing and drying, should be left for a day to enable the protective oxide film to reform through contact with the air.

Coatings

Coat aluminium surfaces with a protective clear lacquer after cleaning. This form of protection is not usually needed unless the aluminium is likely to be affected by salt such as found at a seaside location.