What colour is rust?

When we supply our bare metal cast iron air bricks they are a dull grey colour because they are kept in a dry, warm storage workshop. Obviously that’s the best way to store them so our customers get them looking there best, like the first day they were made . It also means if we are going to paint them then we have a rust free surface to apply the paint to .

We had an interesting question from an architect today, a question that’s asked from time to time…

When a bare metal cast iron air brick “rusts” , what colour is it?

Well, the simple answer, according to the “all knowing internet/Wikipedia” the colour of rust is “brown” . But that is oversimplifying it, the long answer is …

It all depends on how wet it is and how old it is ! When dry and new its likely to be more orange and when old and wet , closer to dark brown . Although iron oxide is the chemical name for rust, care should be taken not to confuse the term “oxide” with a description of the colour. Oxide used to describe paint colour is specifically a red colour and not a close description of the colour of rusty cast iron.  To describe the colour of rust we would say it’s a combination of Red, Orange and Brown , often described by those in the trade as “orangey brown”  but grammatically more correctly described as orange-brown. In fact, as the word rust comes from the Germanic “Rusta” which means ruddy, it could be described as having a ruddiness which broadly suggests redness or reddish tones.