Machine doubling damage (MDD) has been a topic that I have researched and written about for close to 30 years. Curiously it is a topic that has been virtually impossible to "sell" to the collectors and dealers. Since it affects world coins, it will be this week's topic.
Anyone who has looked closely at a quantity of coins has seen it. It's the most common form of doubling found on coins. It has appeared under a laundry list of names, such as "shift," "micro-doubling," "double die," (Not doubled die), "strike doubling" and most recently as MDD.
I have to take the blame for the "strike doubling" title, which I based on some false information given me by a Mint official. It is not part of the strike, occurring after the completion of the strike, so obviously it cannot be strike doubling. The actual cause is the bouncing of the die/die holder assembly on the struck coin. The strike ends with the "final impact of the die pair." Die bounce or chatter involves only one die. While you can find MDD on both sides of a coin, the cause is different on each side as there are at least three forms of MDD, each with a different cause. When I had to 'eat' the strike doubling label, I picked up the MDD name, which was being used by the old ANACS when it was still part of the ANA.
From the very first, attempts were made to claim that doubling was caused by the die twisting at the moment of impact. A little thought will discount that theory, because you are dealing with a die which is meshing with the forming design on the coin under 25 or more tons per square inch of pressure. The amount of force needed to rotate the die under those conditions would run into the thousands of tons. If such a force were available, it would shove the entire design out of position. MDD always affects only part of the design, so this cannot be the cause. To prove my point, hold your hands together, with your fingers interlaced. Now, try and move one hand sideways without moving the other.
The evidence is very clear that MDD occurs after the strike. The coin design is complete, meaning the die pair has done its job. The bouncing/chattering die moves metal that has already been formed. Struck metal has a different appearance than the metal shoved or moved by the bouncing die. Because of this difference it is possible to trace anything that occurs during the minting process. Anything that happens after the strike cannot be traced as to time or place.
Over the years many attempts have been made to sell coins with MDD for substantial prices. Checking the back issues of the hobby publications will turn up prices as high as $75 for a coin with MDD (but hiding behind some nickname). The fact that MDD is damage to the struck coin and reduces the collector value rather than increasing it is a bitter pill to swallow, especially among collectors of some of the early coins where such doubling has been hailed as a collectible for years. Chalk it up to the lack of knowledge of the minting process.