Russian Empire Y#11 - Condition or Other issue??

I have about 6 coins of Russian Empire 3 Kupic Y#11 - although all seems to be in a great shape, some looks like copper - but others are gray/'silvered' as nickle...

Is it just a matter of condition (-but a gray copper!?!) - or maybe it is an other issue???

Thats really weird. All coins in Imperial Russia from 1/2 kopek to 3 kopeks were made of copper. 5 kopek was made of copper (big coin) and of silver (tiny coin, even smaller than 3 pence, closer to 4 pence - groat).

So I assume these grey kopeks are original copper coins that were either painted or plated in some sort of grey metal later, maybe in Soviet era by some person.

plated....