As others have said, this is zinc rot. It's not a mint error.
All I see are stains.
Try this article: http://www.coinworld.com/insights/different-causes-of-stripes-on-coins-are-not-fully-understood.html
The four coins depicted above are a mixture of die caps and capped die strikes. The former are considerably rarer and more valuable than the latter.
As others have said, this is a "squeeze job" (a.k.a., vise job, hammer job, smash job, press job).
Machine doubling, without a doubt.
Odd. My original opinion remains unaltered, but perhaps the folks responsible for this counterfeit strike also happened to select an underweight...
I'm surprised it's underweight. Does it show the copper core on the edge?
Second strike delivered by a pair of counterfeit dies of relatively soft consistency. The warped surface (especially evident on the obverse), the...
I'm not sure what's going on with the Canadian coin, but it's not a bleb. The elevations are too smooth and the die doesn't appear particularly worn.
I prefer "bleb", but it's merely a personal preference. There is no referee that determines which term is "official". Since I'm not a...
Ken Potter calls them "patches". They may be caused by de-carborization of the die steel.
It's highly irregular shape makes this more likely to a "bleb", the positive impression of a die erosion pit. These sometimes develop in late die...
A saddle strike IS a double strike, in my book. The strikes are simply delivered in tandem, rather than in successsion. True, there's only a...
I don't think it's a saddle strike as the wrong part of IN GOD WE TRUST is showing. So it would be a conventional triple strike.
Impact damage from another cent.
These appear to be contact marks from the denticles of a second quarter. It's not a minting error.
The absence of weakness on the obverse face eliminates any kind of planchet defect from consideration. The absence of finning of the obverse rim...
Repunched dates and overdates are very common among Colombian 1 centavo coins of the 1960s and early 1970s. In fact it's hard to find a specimen...
Collar clash together with a finned rim.
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