Luxembourg: 1 franc 1990, km63, die error

[Globetrotter]

A coin with a lot of excess alloy....

[africancoins]

Perhaps this is more likely to be an issue with the plating.

Thanks Mr Paul Baker

[Globetrotter]

Yes, you might be right, but the plating is already there when the coin is struck. So you think there might have been some impurities between the raw slab and the plating, which then shows after a while on the surface of the coin? Would that be some chemical reaction or just some expanding mechanical forces caused by the impurity itself?

[Figleaf]

The Brussels mint had a problem with Cu-Ni coins in the interbellum, with impurities causing cracks and layers of metal coming off. However, the cracks were straight lines and the problem was fixed in the early 50s.

Not sure what could have caused this. I have seen similar oddities on euro-coins, where the problem bubbles were ascribed to oily dies. Can't see the mechanics of that, but there you are.

One possibility in my mind is that freshly struck coins are cleaned with pretty bad acids. If these are not washed away thoroughly, or if some of the cleaning agent spills on the coins after they have been rinsed, you may get this kind of bubble-shaped protrusions.

Peter

[Globetrotter]

here are 2 other examples, but from Malaysia....

[Aernout]

Some examples of the Brussels Mint:

See attachments

mvg,
Aernout