oils on copper is a very oil technique employed in the 16th century. It results on a finished painting that is usually free of all cracking and the colors stay vibrant (Of course there can be dust and grime from years of hanging in smokey parlors).
Some artists have revived the technique for studio painting.(Doesn't do well in plein aire in the cold). Youll see lots of still lives and studio compositions from photos on small copper sheets.
It could be very old or very new.
Sargent used to screw with the metal for a few of his studio paintings but not many as far as I know.