Proof Coins

The UK ones are generally frosted after the NEW PENCE was dropped and its easy to spot. Mirror fields and frosty design. I found what I think is a proof in circulation (perhaps a proof die used to strike business strike coins). A Gibraltar 50p, beaten up. The yanks call them 'impaired proofs'.

Modern proof coins in circulation are, almost always, introduced into circulation via a proof set being broken open and spent - obviously, by a non-collector. This proof set would have been either stolen, or inherited by someone completely apathetic and clueless about coins.


The Royal Mint never does this and, as far as I know, never has. The American mints used to do it, back in the mid-1800s, creating the "prooflike" phenomenon described in the CCF Glossary.

Valuing circulated proofs or "impaired proofs" is tricky, since the catalogues usually only give a value for proof coins in one "grade" - proof. I think the general rule of thumb (here in Australia, anyway) is, unless they're really heavily worn or badly scuffed/damaged, they're worth about a third of the difference between the quoted "proof" value and the face/bullion value.

Sap, is of course right. In addition, proof decimals are struck on specially prepared polished blanks and struck with more pressure (twice?) than the business strikes, the two processes (proof and circulation strike) being quite different. The Royal Mint nowadays have a third method - rather confusingly called BU (Brilliant Uncirculated), which is somewhere in between the two standards.