Perhaps the core of a fourree that has lost its silvering?
Silver is a more noble metal than copper.
The more noble a metal the higher the acid resistance.
That acid or environment is destroying the silver with higher acid resistance much than earlier than copper with lower acid resistence is impossible.
So there is no way that all siver is gone but the bronze is still there and not damaged.
I have several fourrees in my collection they have the normal pattern, there is the silvering damaged on one or more position and there acid/corrosion is eating the copper core, while the silverplating is still pretty much intact, if the copper layer underneath is is gone the silver has nothing to stick on and will be either in air or fall off.
The patina has fine crystalls and is uniform a typical artificial patina.
Finding fouree cores with the silver lost is not impossible, it is actually fairly common, and I have handled them. Many fourrees were struck with a silver foil plating that can be mechanically removed (intentionally or in nature) without significant damage to the bronze core. Two pieces of silver foil are used to wrap the core, one on each side; both folded over to completely cover the core. Sometimes they fuse sufficiently to each other, due the pressure of striking, but are not firmly attached to the core. This is fact proven by many many examples with partial plating remaining.
I am not saying this IS a fourree core but you are wrong in believing that an undamaged fourree core with the silver lost is impossible. They exist.
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