Die-deterioration doubling

Die deterioration doubling (DDD) is an extremely common form of mint-made error on many United States and Canadian coins that results from degradation of the die used to strike the coin.

Due to a combination of improper preparation and treatment of the dies, excessive wear, and overuse, die deterioration doubling has occurred on nearly every series issued by the US mint in recent times. Certain coins are more susceptible to it than others, due to various factors, but it does occur on most series of coins.

During the annealing process of die making, two main errors can occur, resulting in less than perfect dies. It is impossible to tell without expensive and lengthy tests whether these errors occurred, but they will lead to significantly weaker dies and a higher tendency to deteriorate quickly. The first thing which can happen to a die in this process what metallurgists call decarburization. Decarburization is the result of an improper mix of metals and chemicals in the annealing furnace where the dies are sent to soften. If there is not enough ambient carbon in the furnace, the steel will give up some of its carbon and will become soft. The result is a thin surface of inadequate metal whose chemical composition has been altered and is below standard.

Another less obvious error can also occur when heating the dies. After being taken out of the annealing furnace, the dies must cool for 24 to 36 hours. They are usually given an oil bath to cool them more quickly, but the dies must still cool for a period of several hours. When the dies are cooling, if they are not stored properly or not allowed to fully cool before being used, the result is a much softer die. When the die is subjected to the hubbing press again and work hardened again, it will be softer and more susceptible to wear. If the die is softer because it was not fully cooled, it will not harden to the same standard as a die which has received proper treatment. However, there will not be a noticeable difference between a good die and a bad die; the change in the structure of the die does is not apparent until it is used for a period of time.

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