Brass Mack Plaque in Antique and Classic Mack Trucks General Discussion Posted Monday at 10:52 AM Alex I have the same brass plaque, they are rare pieces it seems. Mine was dull and near black with grime, I have done a gentle clean and now looks similar to your plaque. I tried to polish the back side a bit harder to experiment to see how bright the brass may polish to. It did not/would not come up very bright, so I think it may be the quality of the brass made at that time. I cleaned all the grime from mine and it still has the old patina look. I have thought about giving it a clear coat but decided to leave original, been 1 year now and no change in the patina, has not dulled at all.