The cast - iron firebacks that I find when crossing Europe show very different conditions.
Sometimes, a fireback is in an excellent state of preservation. It often origines from a collection and no further renovation is necessary.
In some cases, one of the previous owners has painted the fireback typically using matt or semi-matt black varnish.
This paint coating beeing part of the fireback's history, I normally leave as it is. The paint doesn't affect the use in a fireplace or on a wall.
In the majority of cases, the fireback isn't painted, but simply more or less rusty.
The hole surface is covered by a thin layer of rust, often mixed with traces of carbon black and tar.
After removing greater rust spots using a chisel, the front surface is cleaned by rotating wire brushes until the bare metal glares.
I don't mind little remaining traces of rust underlining the nature of cast iron. The result is a wonderful metallic bright luster.
A fireback treated like that makes you feel the material and the surface structure.
However , a fireback brushed but not painted will probably show initial easily removable rust in the course of time.
Though very effective, I avoid sandblasting to remove dirt or rust as far as possible , as this treatment impaires the surface structure and the patina of a antique fireback.
At buyer's option, I can paint every fireback using a special high heat paint for iron.
As a matter of principle, restoration is limited to the front side . The back side is left in its original condition enabling everybody to get an idea of the real age of the respective fireback.