A patina is the thin surface layer that
forms on many metals due to their natural ageing and weathering.
A genuine patina can take many years to develop, and because of
this, chemical treatments are available to speed
up the production of certain patinas. Different metals produce
different patinas depending on their treatment and the results can be somewhat
unpredictable; creating a patina is definitely more of an art
than a science.
Freshly galvanised steel can be a bit too bright and shiny at times. After a few years of exposure to the atmosphere it will naturally weather to turn a matt grey. However, it can be artificially aged using special acids that will quickly turn it a matt and mottled grey-black that weathers to a very attractive powdery grey-white rather reminiscent of old lead.
Perhaps the best known patina is the blue-green verdigris that forms on weathered copper and bronze. However, these metals can also develop many other rich and varied patinas, ranging from the classic brown statuary bronze through to the deep maroons and reds seen on forged and heated copper.