In a normal strike, the planchet sits nicely inside the collar and the centre of both dies hit the centre of the planchet. A mis-strike is a GENERAL term for any type of error caused by misalignment of dies, collar or planchet.
1) A broadstrike is a strike in which the planchet is struck without the collar being engaged. This strike may be perfectly centred or off-centre. On occasion, this results in a hugely spread flan (much more likely for softer materials such as silver than for harder materials)
|No collar, extremely well centred strike on a florin. Notice how the rim denticles have spread at all points as the metal flow is unconstrained.|
|Slightly off-centre strike on a sixpence, the collar engaging on a tiny part of the rim (obverse from 6 o'clock to 9 o'clock). Notice how the rim denticles on the obverse have spread only in the areas where the collar is not engaged.|
|Well off-centred strike on a shilling, the collar not engaging at all.|
2) A ramstrike is a strike where the collar is present but the planchet is sitting off-centre. A ramstrike will show evidence of the collar (this is particularly easy to see if the collar has milling as for a florin or a 20c). Ramstrikes can be truly spectacular error coins. There are two major types of ramstrike, the first is very scarce, the second extremely rare:
|a) High rim (a tiny gap between the collar and the edge of the die causes metal to flow upwards)|
b) The planchet is a lot further off-centre (this is the most spectacular example it has ever been my pleasure to view)
3) Collar partially engaged. When the coin is struck metal flows outward. If the collar is present the metal flow is constrained, if not the metal flows outward such as in a broadstrike. The result is that the part of the rim where the collar was not engaged extends outwards. If the collar is at an angle we have a tilted partial collar (I have seen many Australian dollar coins of this type), if not at an angle we have what the Americans call railroad rim coins (all the Australian predecimal and 2 cent partial collars I have seen are of this type).
4) Off Centre Die. This is an extremely rare error in modern times (although was common in the era of hammered coins). The planchet is seated within the collar but the hammer die hits off-centre. Note how the base of PENNY is not struck up; this always occurs when the metal flow on the other side of the coin is unconstrained (in this case unconstrained by the obverse die). The only examples of this in the predecimal series that I know of occur for 1946 Perth shillings, 1952 Perth pennies and 1955 halfpennies. As the die has drifted out of line, all coins struck until the problem is rectified will exhibit the same error.
But what about the decimal series? I do not know of any examples where the die is sufficiently off centre to cause loss of detail on the other side of the coin. But very slightly off-centre die decimals, to the extent where the rim is thinner or just missing over part of the circumference, are extremely common, to the point where they domninate the "perfect strikes" for the two dollar series and also the 2004 and 2005 mob of roos dollars.
I have seen them incorrectly advertised as "rare misstrikes" and even more ridiculously as "mule-like" on a particular auction site. As they are considered by the Royal Australian Mint to be within tolerance they should not be classified as an error. Personally, I consider an off-centre die as collectable only when the die is sufficiently off centre to cause loss of detail on the other side of the coin.
Special thanks to Keith Day for numerous discussions on error coins and also to Carlo Margariti for the use of the image of the ramstrike shilling .