Scuff them with a scotchbrite superfine pad (gray). Then shoot a very, very thin coat of self etching primer on them. You should be almost able to see through the primer. Lightly sand with 320 grit paper and knock down the roughness leaving as much primer on as possible. Using multiple thin coats (3 should do it), paint them satin black. I prefer lacquer spray paint as it drys to a smooth finish where enamel tends to glop. Try to never overlap coats; you'll get coverage as you build coats, i.e. if you miss a spot, just get it on the next coat.