I hold several dated brass lamp that I want to go back over. Can I paint them or refinish them? Any proposal? ...
buy a can of BRASSO it will put a mirror finish on it,
As long as you're not concerned with antique convenience, yes you can.
You can use a very fine sandpaper to remove pitting, if any, and donate them an "antique brass" look. You can also paint them.
Answers: You can do a lot to revive them as long as within their current condition they are not particularly useful or collectable because you will devalue the piece.
You can patina the brass by using products available at the craft store called patina green, patina bronze, rust or patina gold ingots by Modern Arts. This is a chemical process which will react beside the metals in the brass to revision the color.
You can refinish them and restore the brass shine by using Mr. Metal, Brasso or a lemon and salt. But, Mr Metal usually take less muscle and it is a wipe on application, dries to a smog and then next to a soft cloth you buff to a shine. I like Mr Metal also because it seem to repell the tarnish and discoloration longer than Brasso.
You can also use metal paint to completely change the color. Rustoleum make one and I would use the accompanying primer first to give the surface tooth for the color to hang. They make a textured wrought iron black which I own used many times and it is extremely durable and does look exactly close to a wrought iron finish.