Probably you shouldn't clean it up....it would hurt the value....
But....I understand wanting it less cruddy.
A very fine grade of steel wool, at least OOOO grade.....and use it with some brass and copper cleaner, like Simichrome.
Linda C

You have to be careful what you do as often you have copper plating over a base such as pewter, tin, etc. You can use a detergent to clean off some of the dirt. Copper turns green with age. If you only want the item for decoration there are various copper cleaners but I would be extremly cautious about using anything abrasive.

The chances of a copper ship's lamp being anything but solid copper are slim to none.
In fact in all my years of collectiung stuff, looking at stuff and seeing stuff, I have never seen anything that was copper plated. I have seen brass plating on cheap lamps and door knobs, but copper and brass are so inexpensive that the cost of the plating process often costs more than the money saved. Copper is the base metal that plating is put over!....Notably silver.
Linda C