by dave-r » 30 Oct 2005 8:56
They are made from white metal aka pot metal. A cast alloy commonly used for chrome trim. When chromed it can corrode in the weather and become very pitted.
Just look at the chrome around a 1970s rear lights. Same stuff and only the ones from very dry climates are not pitted.
Repair and re-chrome is a specialist process and even then only if it is not too bad to start with.