Australian 1979 10c Clamshell Split Planchet

In Part 1 of the Split Planchet Coin Errors series of articles brief mention was made of the so called ‘clamshell’ partially split planchet. This sort of coin error, seen here, happens when there is a weakness in the metal of the planchet and the coin fractures along the weakness. In the case of the ‘clamshell’, the weakness may not run through the entire planchet resulting in a partially separated coin split parallel to the faces of the coin. Typically the side that is split is opened up slightly giving the characteristic clamshell appearance. This type of error is also called a hinged split blank or planchet.

If you peer inside the opening, and you can see clearly on the 10c imaged above, you can see the parallel striations in the metal that indicate its authenticity as a split coin and hasn’t been sliced open in the back shed.

Some collectors of this sort of error may try to encourage the coin to separate completely through mechanical means or perhaps by repeatedly subjecting the coin to freezing temperatures. When the coin does split completely the result is the more typical sort of split planchet error seen in the first part of this series of articles.

1966 20 cent Clamshell Error

Australian 5 Cent Coin Split Planchet

In the previous entry about Split Planchet Errors I mentioned that there were 2 main types of split planchet error coins. Those where the planchet split those coins that were struck and then the coin split. Shown here are examples of the planchet splitting before coin was struck. The thin underweight planchet then being fed into the press resulting in a weak incomplete strike. The metal striations you can see on the reverse of these 5 cent errors are the inside split face of the planchet. The strike on the coin above is so weak that the date is not fully visible and each coin is underweight approximately half the weight of a regular 5 cent piece.

Fiji 1969 5 Cent Error

Australian 1981 50 cent Split Planchet Mated Pair -this coin split after it was struck.

A split planchet coin error occurs when there is a weakness or lamination defect in the metal blank. During the preparation of the planchet strip foreign materials such as gas, dirt or grease may become trapped below the metal surface. This area of the metal will be weaker and may flake, peel or split because the adhesion is poor where the foreign material is. With the example of a split planchet error the blank may split partially or wholly in 2.

The above example is an Australian 50 cent coin error from 1981. It has split completely in half parallel to the faces of the coin and each side weighs roughly half of a normal coin weight. Each piece fits neatly together just like a puzzle and their combined weight is exactly that of a standard 50 cent piece. You can see parallel striations are present on the inner surfaces where the metal has split. This split has occurred after the striking of the coin.

Split planchet coins are more commonly found as just the one side with the matching other side of the coin out in circulation or a collection somewhere. A split planchet will be worth considerably more if the 2 mated coins called a mated pair are sold or kept together. The split planchet is more commonly seen on copper-nickel Australian decimal coins. It’s rarely seen on copper 1 cent and 2 cent or aluminium bronze dollar or $2 coins although these do exist. Pre-decimal split planchet coins are much much harder to find.

If the split were to happen prior to the coin being struck it would result in a weakly struck or blank portion of the coin surface. And of course the coin would be severely underweight. A coin in the process of splitting in 2 may have a clam-like appearance with one edge open like a hinge.

Australian 1944s Threepence Reverse Brockage

Australia 1942I Half Penny Brockage

Australian error coins are a fairly popular collecting theme among a lot of collectors. Among the most unusual of Australian error coins is the brockage. A brockage is what results when a pressed coin fails to exit the press when the next blank planchet enters the press to be struck. The coin that fails to exit the press is usually stuck to the hammer die (typically the reverse), and is known as a “cap” because of the form it assumed (like a bottle cap). So, when the new blank planchet is struck the obverse side is struck with the normal obverse die, BUT the reverse side is struck against the “cap” (the coin that did not exit from the press correctly). So, you end up with a correctly struck coin obverse and an incuse mirrored image of the obverse on the reverse side of the coin. This is known as a brockage.

Often, the cap coin remains on the die for many strikings and the ‘cap’ shape of the coin becomes more and more pronounced and the obverse of the coin becomes progressively more and more worn and smeared as more and more brockages are struck. You can see a nice image of a Die Cap here. As the cap coin becomes more worn the incuse image on the struck brockage become less and less clear and well struck.

Brockages of Australian Coins are very rare and seldom seen. For those of you who are interested in obtaining one then it is best done at Auction. You can expect to pay a premium for Australian Pre Decimal coin Brockage errors.