Strike doubling, sometimes called machine doubling is the most commonly mistaken double die error. Why? Because it occurs during the actual strike process and doesn't involve the actual die. many collectors make the mistake of believing that these are true double dies and sometimes they even pay a premium for them.

   If a die is loose in the press, sometimes it will twist slightly as th hammer die starts back. This causes a shearing effect on some of the relief areas of the coin. Since the hammer die is on the way up and the strike has already been completed when the shearing effect occurs, the term "machine doubling" or "mechanical doubling" is a commonly used term. Since these terms could be ascribed to other parts of the planchet making process, or even the counting process, the term "strike doubling" is a more accurate description. If you remember the PDS system, then you will see that this description relates to strike. Some numismatists use the term ejection doubling. All of these terms, whichever you use, describe doubling caused by the shearing effect of die twist.

    Strike doubling exhibits a flat shelf-like secondary image. True double dies reflect rounded secondary images. The metal on a strike-doubled coin often appears shiny and gives the impression that the metal has been moved. It appears close to the coin's field and not as a stuck up relief. Strike doubling can affect all the letters or just some of them and sometimes it can show up on a true double die. Especially watch for proof coins with strike doubling. Because proof coins are struck under much higher pressure, the shearing effect is more pronounced.

Many various series of coinage are pronounced for strike doubling. These include Mercury dimes 1936 - 1942 and Lincoln cents 1968 - 1972. Sometimes strike doubling will affect only the mintmark, which confuses many collectors into thinking that they have found a RPM. You can see this phenomenon in Washington quarters and Franklin halves through 1964. The shear of strike doubling affects the deepest part of the coin first, which is generally the mintmarks punched by hand.

There are a number of other doubling effects besides strike. These include die fatigue, die polish and perhaps even intentional effects. More on these later.

In closing, I am reminded of a show I once did in Raleigh, where an avid collector approached my table inquiring about double die state quarters. It seems he was in the process of assembling quite a collection. I told him that, while I had examined a significant number of state quarters, I had not had the pleasure of seeing a true double die. I also informed him about the unlikelihood of finding such a specimen, since the Mint was using the single squeeze process. He simply beamed. Beleiving that, indeed, he had been fortunate to discover some true rarities. While not entirely impossible, the rarity of such an event would bring about a quandry within the numismatic marketplace, as some of you may have read about recently. In any event, the gentlman produced a tube containing half a roll of so-called double dies that he had just purchased at the bargain basement price of only $12.50 each. Of course the fact that they were strike doubles was grossly obvious. Of course the greed factor prevented him from acknowledging the truth. He departed in ignorance, $250.00 poorer. Boy, did he ever get one over on that dumb dealer!

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    TCC
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