I have a garden table and four chairs that I bought about 15 years ago. I leave them outside, uncovered all year round in sun, rain and snow, yet they still look as good now as they did the day I bought them. I want to know what they are made of and what kind of paint is on them. They are metal and relatively lightweight. On a couple of spots where the metal has been exposed through the paint, it is a shiny silver colour which never rusts. The paint itself is light blue and it never flakes. The only way to damage the paint is to hit it really hard, and then a bit of the metal may be exposed. The set really is remarkable, and I wish I could remember where I purchased it.
鈥� The correspondent鈥檚 garden furniture is likely to be made of aluminium, a low-density metal that resists corrosion. When metals such as iron rust, the resulting iron oxide flakes off, exposing fresh metal to further oxidation. Unless protected and preserved in some way, iron structures will eventually corrode right through and become physically weakened. This is why checking for corrosion is part of the UK鈥檚 MOT roadworthiness test for motor vehicles.
In contrast, when the surface of aluminium oxidises, it stays where it is, forming a dull protective layer 鈥� although shiny metal is exposed when this is scratched off. Aluminium needs to be prepared with an etching primer so that paint will adhere to it.
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鈥淎luminium resists corrosion and, when oxidised, forms a dull protective layer鈥�
Tough polyester powder paint might have been applied but, if destined for outdoor use, a latex paint would be ideal as it expands and contracts with the big changes in temperature that outdoor furniture will experience.
Mike Follows, Sutton Coldfield, West Midlands, UK
鈥� The furniture is probably made of aluminium, a light metal that develops a protective layer of aluminium oxide when exposed to air. The oxide layer prevents further corrosion because it is impervious to air and water and doesn鈥檛 flake.
The layer can be strengthened by what is known as anodising. In effect the aluminium object acts as the anode in an electrolytic cell and oxygen reacts with it to further thicken the oxide layer.
Another advantage is that the oxide layer can be dyed, so the colour becomes an integral part of the surface structure. This may be the case with this garden furniture. In this way, aluminium objects can be given attractive, coloured finishes that can withstand weather and children.
David Muir, Science Department, Portobello High School, Edinburgh, UK
This article appeared in print under the headline 鈥淢ade to last鈥�