Brass is an alloy of zinc and copper and without a lacquer finish it will tarnish. When a fixture says it is "Solid Brass" it just means that it is entirely made out of brass without any other metals…it is not actually solid (or it would be too heavy). Brass plated is usually a zinc or aluminum base with a brass coating. Brass plated doesn’t make the top of the list in this situation because you have 2 coatings that could peel and/or tarnish. I would use a fixture that has "Solid Brass" listed in it’s description and be sure to make sure it has a weatherproof or strong lacquered finish. There are a variety of fixtures out there that meet these requirements. Check out Minka’s Great Outdoors line or Quiozel’s Outdoor line.