Bright Blue Verdigris?

On the bottom left it looks like acetate crystals, caused by copper being submerged in vinegar and then being oxidised-if you dip it in water they may disappear like the clean lower half of the coin. So in other words vinegar and evaporation make this reaction happen. On the right it looks like oxidised copper, just like the copper strips(lightning conductors) you may see on old buildings(Cathedrals etc).

I would conclude someone was experimenting with different variables using copper, to see what the results/outcomes would be.

Edited for clarity.

I'm not recommending cleaning coins, just making the point of the crystals being soluble in water. I can understand why you would want to rid these coins of the oxidisation/acetate crystals, but maybe they could be an oddity? If you really want to, I here acetone is probably the best method as it shouldn't affect the coin, only rid the coin of bit's of glue/oxidisation etc. As many members have said to me cleaning is a no no, I'd hate to endorse cleaning-maybe await another members input before breaking the golden rule- 'Thou shalt not clean thy coins, unless uncleaned ancient'.

Acetone won't touch oxidation and won't dissolve salts; whatever the exact composition of those crystals is, these are basically salts. The dark blue crystals do look to me like copper sulfate, and that could form simply by leaving the coin dry in dilute battery acid.

Different soils can make different coloured verdigris when coins are buried in them, based on different and complex chemistries. Blue is not unheard of. "Blue patina" is fragile and highly sought after on ancient coins.

Verdigris can also turn blue if its subjected to a botched cleaning job. I know "normal" green verdigris can turn bright blue if it's soaked in ammonia.

I see. I guess I'll just leave it like that then. I don't think I have anything to clean it with if acetone won't work.

Verdigris is a complicated mixture of various copper salts. It can take on a huge range of colors (in the blue spectrum) based on the dominating composition and hydration state.

Verdigris at the advanced stage shown in the pictures is irremovable without revealing damage to the coin surfaces. Any attempt at removing it would be a futile exercise.

I think a fun project would be to cover as many colors as you can. I think I'll start doing that myself! 2x2's are cheap and it makes for an excellent conversation collection as verdigris is something that affects (or infects, lol) all of us copper collectors.