There are quite a few experimental planchets for pennies... more than any other denomination if I recall. Not sure when their prime time was... I know there was a brief span that they came out more than others. I would throw it in a little envolope and store it away until you run across a dealer or collector in person who has some SERIOUS knowledge in the planchet field. And I mean serious knowledge... I've brought some of mine to dealers who weighed it, looped it, and I even let one of the coins be scratched tested by a couple different dealers, and most say well... I have no idea... it doesn't seem like a normal paint job/coating issue... and then they tell you store it away for a rainy day. These people aren't experts in planchets... just coins. Not many people with the required planchet knowldge.
That is what I have done with a few coins that seemed like they COULD be experimental planchets... just stored them away for a rainy day.
Between dipped/painted coins... think chrome/gold/mercury dipped/coated halves and the common science room experiments... there isn't really much you can do to find out what yours is and you don't have good odds that they are experiment planchets. New planchts don't have many copies made, and so very few get out... especially one as obvious as a silver looking 1957 penny. For example, one of the ones I am keeping is a state quarter with full silver rim that has no signs of a dipping or painting, etc. 99.99% it is just an oddball one that has its copper not showing on the rim for some reason... but it doesn't hurt to store away a quarter. I mean... is it worth spending a hefty sum to get it graded with those odds?
Good luck with getting more info... and let us know if you find out something... one way or the other.
Good luck!
~Dave
