Other British error coins
Quality control on British coinage is very tight and so error coins are a rare occurrence.
However, in 1983, The Royal Mint made an error with the 2p piece and struck some with the wording ‘new pence’ rather than ‘two pence’. The 1983 2p mule is currently worth a couple of hundred pounds, but we don’t really know how many of those were minted (they never entered circulation and only appeared in special promotional packs but, crucially, not every pack had one).
Two Pence coin dated 1983 but with 'New Pence' on the
reverse side: one fetched £600 at auction last year.
Here are the details of some other types of error coins:
Date errors
Date errors occur at the design stage of coin production. When a coin is designed those designs are proofed (checked) and date errors are normally spotted before an incorrect design goes to mint. In the case of the United Kingdom 2009 20 pence piece error the date was missing altogether, an extremely rare occurrence in modern coinage.
Planchet errors
Planchet errors occur when the wrong coin blanks, or planchets, are fed into a coin-stamping press. This results in a coin that has been stamped with a design intended for a differently sized coin; this is called a wrong planchet error. In addition, unminted or blank planchets are occasionally produced. The results are usually obvious errors that are also prized by collectors, though the errors are usually caught in manufacturing and destroyed. Blank planchets with rims are valued lower than those with no rim.
Coin blank for a fifty pence that escaped the Royal Mint having not been struck with the design.
Hub and die errors
Hub and die errors are the result of faults in the coin hub or coin die. There are many different kinds of such errors. Modern coins are still released with hub and die errors, because the defects are too small to be seen with the naked eye.
Strike errors
Strike errors occur when the planchet is struck. It is a fault in the manufacturing process rather than in either the die or the planchet. A standard type of strike error is a broadstrike, where the rim image is not struck into the coin's edge because the collar die was missing. Numismatists often prize strike error coins over perfectly struck examples, which tend to be more common, but less highly than die error coins, which are usually rarer, making it valuable.
Two Pence coin struck off-centre and a section was 'bitten'
by the dies when it did not eject properly.
One pence coin where the blank was not aligned correctly
when the design was impressed.
Twenty pence coin struck on a copper blank
intended for a 1p coin
Overdate
In the past, it was a common practice for a mint to use a certain die until it broke. As some dies would last for multiple years, a figure would be punched over the old date.
Numismatic value of error coins
Most error coins demand a premium when sold, if they are modern coins, dependent upon the rarity of the type of error as well as the rarity of that type of error on a particular denomination. The value of error coins has been subject to much debate and the value is usually determined between the dealer and the collector. Conversely, errors on ancient, medieval and higher value coins are usually detrimental to the coins numismatic value.
Defective die
A coin shows a raised line on its surface. This is caused by a crack in the die used to strike the planchet. Coins sometimes show an unstruck area resulting from a break in the die.
Lamination
A coinage defect consisting of a portion of the metal separating from the rest due to impurities or internal stresses. Lamination flaws occur primarily when a foreign material or gas oxide becomes trapped within the planchet (the metal blank used as a coin).
Brockage
A mirror image of a coin has been struck on both sides of the planchet. This error typically occurs when a coin remains on either die after striking. The second coin receives the image from the die, though its blank other side also receives the image of the struck coin. The result is an incuse mirror image, and the coin is known as a brockage error.
Multiple strike
This occurs when the coin has an additional image on one side from being struck again, off center. The result is sometimes mistaken as being a "doubled die". Note: Also referred to as 'double exposure.'
