This 1943 Lincoln cent is struck in steel but is plated with a combination of 90% zinc, 4% antimony and 6% iron. It was recently discovered in the family of a former Philadelphia Mint metallurgist and was the subject of an article in the September 21, 2009 edition of Coin World.
It differs from the regular zinc coated steel cent of this year in that the plating includes antimony and iron. According to researcher Roger Burdette, it is probable that the antimony was added to make the coin darker in color in order to make it less likely to be confused with a dime which, apparently happened often.
This particular piece is listed as RB43-81 in "United States Pattern & Experimental Pieces of WW-II by Roger Burdette. According to the book, experimental 1943 cents were also struck in the following alloys. Descriptions include Roger Burdette numbers.
Zinc coated steel treated with "Cronak" - RB43-76
Zinc coated steel treated with "Iridite" - RB43-77
Copper plate steel - RB43-78
Steel - RB43-79
Antimony coated - RB43-80
Molybdenum coated zinc plated steel - RB43-82
Precolored zinc coated steel - RB43-83
And several different shell case copper alloys of 90% copper, 10% zinc, 85% copper, 15% zinc and 70% copper and 30% zinc - RB43-84 - RB43-90
It is not known if any of the pieces listed above exist although StacksBowers did sell an example of a copper-zinc alloy which did not match the 3 alloys listed above.
The illustrated piece was last offered as part of the Geyer family Mint error collection in Heritage 11/13 sale and also included a copper plated steel planchet for an RB43-78.
It has not yet been determined how to include these in the Judd pattern book beyond the existing piece.
Photo courtesy of Numismatic Guarantee Corporation.