If you live in the UK you can get a spray paint that is for high temperatures, i.e. fires and barbeques. We got some for our fire at Homebase. Sorry can't think what it is called, but it was on the same shelves as metal paints and sprays.
Hi Casabella
When I was in the Fire Service, there used to be a fire retardant paint called Timonox - don't know if it's still available. Suggest you try Googling it.
Good luck
FBG40