Blanks and planchets quite literally experience a rough-and-tumble existence before entering the striking chamber. At almost every step of the way in the production process they jostle against other planchets and machinery, picking up numerous nicks and dings. These “tumbling marks” are acquired as planchets travel along conveyors and as they’re dropped into hoppers and tote bins. Additional hits are delivered as the planchets tumble around a rotating annealing oven and inside perforated metal cylinders that spin the planchets through a quenching bath, a chemical rinse bath, and a dryer. Impacts also occur as blanks and planchets pass over screens that weed out misshapen, oversized, and undersized planchets.
It’s likely that most tumbling marks are acquired in the annealing oven. I’ve drawn this conclusion because many copper-plated zinc cent planchets lack tumbling marks. These planchets are neither annealed nor do they pass through a chemical rinse bath. They are, however, screened by riddlers and dumped into coveyors, hoppers, and tote bins. It would appear that these pieces of equipment pose a lower potential for harm than the annealing oven.
However they’re acquired, tumbling marks are erased during a normal strike. They will remain visible if a coin is weakly-struck or struck off-center.
Every once in a while you’ll find a weakly-struck coin or an off-center coin that shows no evidence of tumbling marks in unstruck and lightly-struck areas. These coins present a persistent mystery.
Our first example of such a coin is a Roosevelt dime planchet that received an exceedingly weak 70 percent off-center strike that is almost entirely restricted to the elevated proto-rim. The planchet has a bright, gleaming surface that is devoid of tumbling marks. The pristine surface instead shows fine parallel streaks that represent roller marks picked up in the rolling mill.
On a 1986-P Jefferson 5-cent coin, the design didn’t strike up completely, leaving the original surface of the planchet preserved in the center and around the periphery. Once again, the original planchet surface is smooth, bright, and shiny, with no tumbling marks. Fine roller marks persist in most of the poorly-struck areas.
A 1978 5-cent coin presents a very similar appearance.
I see at least four possible explanations for such pristine planchets. These explanations are not necessarily exclusive.
(1) They were just lucky, and simply avoided picking up any tumbling marks.
(2) They skipped a particularly injurious step in the minting process, such as annealing.