Hi, Wick. The varnish will protect the brass and keep it from tarnishing but the color will change and it will not look like brass. Lacquer will make the brass look better and also protect it. I assume that you are doing something like a brass kickplate or house numbers on an exterior door. The usual and best procedure is to varnish the door and lacquer the brass before you attach the brass parts to the door. That assures that the wood under the brass is better protected from the elements also. If you are doing something like a brass inlay on a piece of furniture, doing the whole piece with lacquer is a good option.