Brass

[Bill Shields]

ah...well...someone is assuming that the bell is mounted somewhere other than the front door of an Alaskan homestead....

[James Powell]

"...but it ain't no good if you're in the Jungle..." (Roosevelt E. Roosevelt)

As a sailor who has had to polish the odd bit of brass, elbow grease is the answer, unfortunately. Brasso works, but as noted ^, is not the best. Autosol (?) the paste in what looks like a toothpaste tube was better.

[Bill Shields]

Then there is toothpaste for polishing brass ..also works as lapping compound.

[timmy wheeler]

.....and it leaves it minty fresh

[Rwilliams]

I have used clear acrylic nail polish on small brass parts with good results.

Dick Thomas of GGLS had a small Pacific with some custom cast builder plates. I asked him one time as to how he kept the raised lettering of the plates so nice and rich in color. His answer was surprising, He had the plates cast in gold and therefore, they never would tarnish.

[gwrdriver]

Some years ago I had a number of old school (ie, magnesium) plates photo etched (a la Robert Dustin), and to prevent them oxidizing over time I took them to a local plater and had them nickel plated. The results were excellent and the plating encapsulated the exposed magnesium and has never shown any deterioration.
PS - As I recall, the magnesium had to first be copper plated, and then nickel plated, otherwise the nickel wouldn't adhere.