Black wash over R-O multicolored textured paint

I painted a cast iron table base (looks a bit like an old icecream parlor table) with a copper color Rust-Oleum multicolor textured paint.  Turns out I don't like it as much as I thought I would and I think I would like to add a back wash to give definition to the table because it is ornate. Can I do that and if so, which paint would I use and where would I find the instructions for that paint?

Best regards,