In 1943 there were experimental steel cents produced. I believe this is an experimental steel cent comprised of zinc, antimony and iron which causes the steel cent to be darker in color. Since there are areas on the coin that appears to have not been affected by the corrosion and has a greyish look is evidence of a metal that doesn't corrode easily, as in antimony. The weight of this coin is 2.7g. The third pic is of a chunk of antimony. It takes nitric or sulfuric acid to dissolve antimony. Anyone knows about experiment coins? Comments welcome?
Here is some googled info https://coins.ha.com/itm/patterns/f...-collection-ngc-total-5-pieces-/a/1136-2382.s Here is a certified Tin 1943 https://www.coinworld.com/news/precious-metals/1943-lincoln-cent-mostly-tin-and-antimony.html
Only way to know if it really is an off-metal experimental planchet is going to be by actually having the composition checked. A visual impression isn't good enough. Until a composition check shows it to actually be something else it is just another zinc plated steel cent. Wear, oxidation and dirt can also cause them to be darker.
First step would be to find someone who has an XRF gun and have them shoot it. Best place to find someone who has one would be jewelers that buy scrap gold, large pawn shops, or a larger "we buy gold" establishment. The guns aren't cheap so it needs to be someplace that does a lot of volume to justify their cost. Another possibly location might be a scrap yard but you have to be careful there, some use a different type of tester that actually uses an electric arc to vaporize a sample for testing. It would allow for a deeper test than an XRF gun, but it is destructive to the coin. If an XRF gun result shows a significant antimony response then it would be worth sending to a grading service requesting a composition analysis. They have access to non-destructive equipment that can test deeper than the gun.