Black spots on brass ammo and clip - General Ammunition Discussion

So I bought this ammo about a month ago, and have seen black spots appearing on it ever since. Finally, I decided that I should get advice about this. Here are some details: The ammo is made out of brass, and so is the stripper clip The ammo and brass is fit for the Arisaka 99. The ammo is 7.7x58. These were made in the 1940s They’ve been out in the open most often Here is a picture These are not hair, I can’t rub them off. But if you can answer, it would be greatly appreciated.

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