If that is what I think it is, I used to make them all the time. It looks to me like it is coated with mercury.
this is an error coin I havein my collection one that is in better conidition. In 1948 the war had been over already for 3 years but much steel was still in the molds so some 1948 pennys were molded in that way.
There is no 1948 steel penny and the "molds" (dies) would be different because it's a different year. You have the wrong information.