Tarnish can occur in one of 3 ways. 1) a slow natural general chemical reaction of the alloy with surrounding elements , mostly oxygen and sulphur. 2) a more rapid localized chemical reaction of the alloy due to a corrosive substance coming in contact with the alloy. 3) a localized slow to moderate chemical reaction of a specific section of the alloy that is imperfectly blended or has impure inclusions.

The first picture looks to me like a drop of something corrosive has, preferentially attacked the copper. The rusty looking brown stain is a primary stage of copper oxidation, the more green areas are caused by longer contact with the oxidizing agent. Kind of looks like something landed on it and then the drop ran. Where it landed sustained minimal oxidation but where the drop settled to and crystallized , there was continued lengthy corrosion until the substance was exhausted-----with some bleeding of the reaction around the perimeter.

The other might have the same origin but with a smaller amount of material that didn't run so much.

Groove juice will take a good deal of this away, with likely some pitting and a general loss of the cymbals built up patina. Spot treating will look just like spot treating.

Now thats about as detailed of an explanation as one could ask for, I'll try the grove juice. I believe its acid based no?

Not sure , but it would seem so. The only problem I encountered was that it needs to be removed almost immediately. I spread it smoothly , then rinse it off quickly .

I often wonder if this is caused by bodily fluids emitted while playing such as sweat, blood or blister fluid from the hands. It sounds nasty but it happens. I have an A mini cup ride that I got used and it has the green crud on it and the pattern is consistent with something squirting on it. We as humans can be rather corrosive to metals too. Just a possibility.

Looks to me as stated above that it started with a big drop of sweat. Some folks ph is very acidic. Mix up a teaspoon of baking soda in a few inches of water in a glass and dab some on the spot with a q tip or napkin. If it is acidic the baking soda water will neutralize it. (it will foam up) The same solution will also clean up corroded battery terminals and the mess caused by too old batteries left in electronic devices.