I had a few older cymbals that were pretty grungy looking, and picked up a few more recently that also looked pretty dingy, so I did some research here and other places, and decided to try it. I figured on the newer ones I had just picked up, I wasn't out much, if anything, they weren't regular on my kit so I would experiment, and maybe learn something.
There are so many testimonials here, and other places, that info overload starts to set in. I decided to try a cut lemon, and Bar Keepers Friend.
The lemon did a good job brightening up older cymbals, but didn't really help with the heavy green stuff.
BKF did a great job on the heavier dirtied ones. I discovered right away that it would take the logo off, it you didn't pay attention to what you were doing. (That particular cymbal still has the logo on the underside, so it wasn't as big a deal. I like having the logo's myself...) I learned how to go lightly over the logos after that
I was curious about the perceived difference in sound that some had mentioned. None of my gear is particularly high end, nor are my ears trained to notice the differences, I suppose. (I know what I like to hear, that's all I have to work with.)
I only did the smaller cymbals in my collection. My 1980 New Beats, as well as some 14" and 16" lower end Zyldjian and Sabians.
I didn't notice anything that I could tell for a difference sound-wise in my gig last night. I prefer a brighter cymbal sound myself, so perhaps that is why. If there is a descenrnable difference to some, that is.
I really did enjoy seeing those cymbals bright and shiny. Dunno why, I just did. I sat there looking at those old New Beats on the hats all night, and they looked practically brand new.
Now I'm sold. Just a little apprehensive going after the old bigger Zildjians, 18" Crash/Ride and 20" Ride. Fortunately with the experience I got from the smaller cymbals, I think I'll be fine.
So my findings are to freshen up a cymbal, lemon works fine and has less chance of affecting logo's. Heavier dirt and staining, use the BKF and be careful around the logo's.