By Irene A. Blake, Updated Aug 30 2022
A penny does not truly “rust.” The thin copper plating on the coin gradually oxidizes, forming a greenish patina. This oxidation occurs when copper reacts with oxygen, moisture, and carbon dioxide in the air. Rust, in contrast, refers to the iron‑oxide reaction. In this guide we’ll show you how to accelerate the oxidation of a penny using everyday kitchen ingredients.
Place a copper penny in a shallow bowl or on a plate outdoors. Check the coin weekly to observe the slow progression of copper corrosion. The process is noticeably faster in humid climates or near the sea.
To speed up the reaction, lay the penny in a bowl.
Sprinkle ½ tsp of salt over the coin, then cover its surface with vinegar or freshly squeezed lemon juice.
Let the mixture sit for 5–10 minutes, then remove the penny and blot it dry with a paper towel.
Within the next hour, the penny will transition from a bright, shiny appearance—thanks to the acid stripping away surface grime—to a greenish hue as copper oxidizes.
Safety Note: Wear gloves and work in a well‑ventilated area to avoid inhaling fumes from the acidic solution.
