So I experimented with black spray paint wiped off immediately with a paper towel. That was on the crater one. It's OK, but not great.
So with the second one, I put a heavy coat of black paint on it an allow it to dry.
It's drying now, and I'll go down later to sand the high spots down to bright bare metal. I'm hoping it will look really good with the contrast between black and bright shiny metal.
Hopefully more soon...