Doubled die
The error in question occurs in the production phase of the die, and in particular in the process of transferring the image from the hub to the die to be used in the money press.
The dies are made through a hydraulic press which compresses the hub against a slightly pointed metal cylinder (virgin die) with a pressure of hundreds of tons. Since a single compression is not usually sufficient to transfer the image to a satisfactory quality level, two or even more compressions are usually performed.
In this regard, it should be noted that, due to the hardness of the steel of which the die is made, the subsequent compression is unable to totally cancel the previous compression. Consequently, if the hub and the die are not aligned in one of the compressions subsequent to the first, the image of the die will show at least some signs of the previous compression (so-called "doubling effect").
The doubling effect can affect the entire face of the die or only one area (generally located in the center of the die). In particular, the latter case can occur when a first partial misaligned compression is performed, ie the hub is not pushed "all the way", and since the virgin die is slightly pointed, only one area of the die is compressed.
Depending on the type of misalignment, about 8 classes of doubled die can be identified.
Class I - Rotated doubling: the first compression of the die occurs normally, while in the second compression (or in subsequent ones), the hub is rotated on its axis clockwise or counterclockwise. Therefore, two split images will appear on the die and on the coins minted from that die, expanding clockwise or counterclockwise. The second compression will create the strongest impression. The point of rotation is usually the center, but nothing prevents it from being any point on the surface of the die.
Class II - Distorted doubling: This class occurs when a hub is used in one of the compressions that has distorted in width. This can happen when the hub is used for a long time, even to create hundreds of dies. In fact, in this case, the punch tends to stretch slightly, to widen and the image will be slightly distorted and stretched outwards. If the distorted punch is used in the first compression, the doubling effect will tend to expand towards the center, if the distorted punch is used in the second compression (or subsequent ones) the doubling effect will tend to expand towards the edge. In these cases, the doubling effect is minimal and is more noticeable in the figure or in the writings near the edges.
Class III - Doubling with different imprint: this class occurs when a hub is used in one of the compressions that has one or more elements (e.g. digit of a date, letter of a word, mint mark, signature, etc.) slightly different or positioned differently.
Class IV - Displaced doubling: the first compression of the die occurs normally, while in the second compression (or in subsequent ones) the hub is displaced on its axis in any direction. Unlike rotated splitting, in this case the die axis does not rotate on itself clockwise or counterclockwise, but moves entirely in a specific direction (from the center outwards).
Indeed, it is not possible to establish whether it was the die or the hub that was moved, but by convention the movement is attributed to the die (E.C.71 and E.C.72).
Class V - doubling with pin: the first compression of the die occurs normally, while in the second compression (or in subsequent ones) the hub is rotated or moved by pivoting on a point on the face of the die, which is usually placed near the edge .
In this type of error, the doubling effect opens "like a fan" from the point that acts as a pivot. In other words, near the pin the image will be "normal", but - as you move away from the pin - the expansion between the two images increases until reaching the maximum width at the point opposite the pin .
In addition to the five major classes just analyzed, there are also three minor classes.
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