Bill, unless we analize the metal we may never know for sure; but I vaguely recall reading somewhere that these letters were gold. Personally, I don't see copper or brass being used (especially copper) due to the fact that those metal are prone to tranish and even turn green over time. Keep in mind that Hunter used a variety of colored gold in their inlays; and also that carat weight impacts the color of gold. Although I cannot verify this information, I have been told that the gold bar rib inlays are 10 ct. If you ever have a chance to examine one of Hunter's gold pigeon rib inlays next to the gold bar rib inlay, the difference in the color of the gold material used for each type inlay is very obvious.