That’s a big bucket lister, huge congrats! Have you found/cleaned many large cents in your area? In PA some old copper coins have that coating of crud that your coin appears to have and can be removed to expose nice details with a toothpick or Andres Pencils (soft one only). Other old coppers only carry the detail in this crud layer and when removed the coin is truly ruined. Others on this forum use a peroxide technique and some electrolysis. Maybe best to meet up with someone in your area who has cleaned a rare old copper before attempting.