In recent months I've received numerous coins for examination that the owners thought were hub-doubled dies on 1999 Jefferson five cent pieces, 1999 States Commemorative Quarters and Canadian Millennium Commemorative Quarters. In fact, the coins did exhibit a common form of die doubling that appears somewhat similar to but is clearly not hub-doubling. Rather than hub-doubling, the coins exhibit doubling, thickening, twisting and other deformities which results from die deterioration. Die deterioration is the result of die wear or improper heat treating (of the dies) combined with die wear. These variations, which I will refer to here collectively as "Die Deterioration Doubling" (DDD), are most often displayed on the date and motto and other characters around the rim of the die but occasionally extended into central designs on more extreme examples.

On the other hand, hub-doubled dies (commonly referred to as "doubled dies"), are the result of the multiple hubbing process. Hub-doubling is possible on many world coins due to a phenomenon known as work hardening, which causes the metal of the face of a die to become too hard and too brittle to allow a complete image to be sunk into a die in one operation. Several impressions or hubbings are required to produce a die using the multiple-hubbing process. (In recent years, the multiple hubbing process has been replaced by several world Mints, including the United States Mint, by the more modern "single squeeze" restrained-hubbing process which eliminates the possibility of hub-doubling). Between each hubbing the die is removed from the press and annealed (softened) thus allowing for another impression without shattering the die. If a misalignment of images occurs due to improper indexing during the reinstallation of a partially finished die into a hubbing press for a subsequent impression, a doubled die will result.

Since DDD is rather prolific this year, now is as good a time as any to review what we have learned about this form of die-doubling in the past so that it is not mistaken for hub-doubling by newcomers to the hobby today.

DDD is a term I originally borrowed from Canadian numismatics to replace other terms such as "polished die-doubling", "die fatigue doubling" and "decarburization doubling", which I felt less comfortable with but were in usage in U.S. circles in the early 1980s and earlier. As far as I've been able to ascertain, the term DDD was originally coined by Jack Forbes back in the late 1960s in Unusual Canadian Objects, (a magazine edited by Canadian error-variety coin pioneer, Hans Zoell). The following quotes are excerpted from Forbes and Zoell's 1970 Fifth Edition of Canada Minor Coin Varieties. In the chapter entitled, "New Information" on page 8, Forbes states:

"Coins struck with deteriorated dies can be attributed to mass production. (The) most common denomination is the 5c, followed by the 1c of the more recent issues. Once the plated surface of the working die weakens, continued deterioration will set in. It is believed that the progress of deterioration is quite rapid, likely reason for an inspector to take note in time, to prevent this imperfection in the manufacture."

Still later on page 12 in the chapter entitled "Re-entry, Re-cut, Die-shift, Deterioration", Forbes says:

"Die deterioration is another form of doubling, again similar in appearance to a re-entry ['Re-entry' was Forbes' term for repunching and hub-doubling - KP] to the naked and inexperienced eye. There is a great difference however, in that this doubling is not sharp and that the outlining is sometimes visible on both sides of a character, although, always strongest on the side toward the outside rim of the coin. In most instances, deterioration is noticed first on the very edge of the die, near and between the beading or teething, but seldom around the full circle."

Forbes' insights into the DDD question are as valid today as they were when first presented. However, additional research has revealed more on the exact nature of the causes and why it manifests itself differently on various designs and on different metals struck. It is also important to note that DDD is often more pronounced on Canadian coins (and other coins) struck with chromium-plated dies and that the effects will vary between processes.

While die deterioration has certainly been a factor in coinage for as long as coins have been struck, DDD on U.S. coins seems to be most prevalent on the 1943 zinc-plated steel cents (undoubtedly due to the hardness of the steel planchets), other Lincoln cents starting in about the 1950s through present, from the early 1960s to present on five-cent pieces and from 1965 to present on the cupro-nickel clad coinage.

Shown in this first installment of the series are examples of DDD on two different 1999-P Jefferson five-cent pieces. (Picture below.) The upper piece was sent in by Marc A. Gennesse and shows doubling on the date and all lettering about the rim. The lower piece was sent in by Jack Martin and exhibits doubling on the Mint mark.

Readers should compare the doubling on these coins to that on the Mexican 1979 20-centavos doubled-die obverse also shown.(Above.) Note the distinct overlapping of images on the doubled die vs the characteristics described above for DDD.

In the next installment we will examine, in greater depth, some specific causes of DDD (other than die wear) and look at some more of its effects.

Ken Potter is the official attributor of world doubled dies for the Combined Organizations of Numismatic Error Collectors of America and for the National Collectors Association of Die Doubling. He also privately lists other collectable variety types on both U.S. and world coins in the Variety Coin Register.