This article gives out information on types of error coins. As the number of error coins classification is quite large, the article is divided into 6 Parts.
Part 1: Design Errors
Part 2: Die Making Errors
Part 3: Planchet Errors
Part 4: Strike Errors
Part 5: strike Errors Continued
Part 6: Mules
Struck on Wrong PlanchetThis type of error occurs when the wrong size of planceht find their way in the striking chamber. For example a One Rupee Size planchet is put in the Two Rupee stamping press. This results in partial minting of the coin. There are multiple places where this can occur.
- During the planchet making process, after the blanks are punched, some blanks are stuck / left over and get collected with the next lot of planchets.
- During storage process, few stray planchets collected are tossed into wrong bins.
- During the feeding process, the operator has put in a different lot of planchets. This typically happens when the sizes of the coins have got changed and operators make mistakes. However when such a error happens, the number of coins minted on wrong planchet are high [entire batch loaded] and get caught and the entire batch scrapped. However at times few may find there way into other batches and don’t get discarded.
- In the stamping press few planchets from the previous run of different size remain. When the press is prepared for strike of different denomination coins, these find their way in striking chamber.
A new Rs 2 Coin on Rs 1 Flan
A Rs 2 RBI Commemorative on a Rs 1 Flang
A Rs 2 Cupro Nickel on a Rs 1 Cupro Nickel Flan. Its very difficult to notice this error as the coin size was almost same [Rs 1 is slightly smaller]. The only way to identify is look at the edges. The Rs 1 is circular and the Rs 2 is 12 sided.
Normally the Obverse and Reverse images of a coin remain upright. IE If one flips [rotate by 180 degree around the vertical axis] the coin the image is still upright. In a rotated die, the images are offset by various degrees. At times the rotation is as less at 15 degrees, at times 180 degrees. There are cases when the rotation is more than 180 and is nearly 350 degrees.
The Maharana Pratap Coin that was rotated by 15 Degrees.
The 1992 Coin that was rotated by 180 degrees
In this type of error, a Blank [or previously stuck] Planchet [Coin] partially Overlaps another Planchet that is being struck in the striking chamber. The coin stuck will exhibit a blank area often at reduced thickness due to the pressure of the overlapping coin. The coin being stuck can be centred or off-centred.
There are always 2 coins involved in an Indent and both will show different errors.
Typically Indent errors occur with double strikes and depending on the sequence of strikes, different combinations are possible.
In the coin below, this was stuck only once; this coin was complete centred in the strike chamber. There was another coin below overlapping partially as well. The pressure / thickness difference caused the indent on this coin [notice the first image]. The other coin will also show an indent and a partial image on it. Notice the Obverse, the image is centred by only partial image is stuck. This is because of the difference in thickness, the coins do no lie flat, and hence the die is not able to put adequate pressure on this portion.
Off-centred strike to Indent with Double Strike
Here on the first strike, this coin was not completely in the strike chamber. This coin would on first strike cause an indent like the one above [Figure 1]. After this strike, the other coin would have got ejected. The image till this point in time on the coin would be only the indented one as seen in the second image. All other portion on both sides would be Blank. This coin has now moved into the strike chamber, centered. The second strike would now put all the other details.
Centred Strike with subsequent Indent:
Here the coin on first strike was stuck as a normal centred strike. However instead of getting ejected, it stayed in the strike chamber. Another coin got partial deposited in the strike chamber. The second strike created the indent on one side, as also overwrote partial details on the obverse.
Incorrect Die Pressure:
Normally when the coins are being stuck, the press holding the die comes down with a specified pressure on the Blanks creating the impression. Sometimes the die pressure is less due to malfunction or during shutting down of the press. Typically when the press is shut down, it may still hit few blanks before coming to stop.
This also happens when there is too much of Oil [used for lubrication and coolant] in the strike chamber. This reduces the pressure of the die on the planchet being stuck.
As described in the die pressure error, this can happen during the time press is being stopped. Normally this is a known issue and the mint staff takes enough precautions to discard such coins.
This type of error occurs when the hammer die comes down on the Anvil die without a planchet to be stuck. The dies thus leave a weak impression of on each other. When the coins are minted with such pair of dies, they would show up the other images with weakness, also these would be mirror image of the actual images.
Apart from the doubling described that typically happen as Die errors, doubling errors can happen during strike as well. A common doubling of this type is when a worn die is used and it retracts faster than desired. The retraction pulls off some part of the metal that has not yet cooled, and the remaining part keeps flowing into the die.
Double Headed: Sholay Coin
This happens when instead of using an Obverse and Reverse pair of dies, the operator at the mint by error mounts both the Obverse or Reverse pair of die. Such types of errors are very unlikely today as the mounts of the Obverse and Reverse dies are different and reduce operator errors. This type of error is possible in older coin. There is no known coin of this type of error in Indian coinage. There are quite a few such fake coins minted to dupe collectors or used in magic tricks.