These are the horns I play regularly. On the left, a Reynolds Contempura dual-trigger bass. In the middle, my beloved King. To the right, a Holton TR-161 large bore tenor, with F-attachment - my symphony horn.
Here is a closer view of the bell sections. Each of them is special, in its own way. The bass bell is either pure copper, or a very copper-rich alloy. It is extremely soft and easily wrinkled, as I once learned to my chagrin. The king bell is sterling silver - heavy, man. The Holton has a rose brass bell. This is a higher copper alloy than yellow brass, and is supposed to deliver a dark, rich sound at lower dynamic levels.