Usually, people look for ways to remove tarnish from their silver jewelry, utensils and coins. But when attempting to produce an aged look, tarnish can be a good thing. Purposely tarnishing coins has become a trick of the trade for coin collectors and hobbyists. Most tarnishing methods require harsh chemicals that can damage the coins. However, there's a simple method that requires only an egg, a jar, the coin you wish to tarnish, and a short length of time.
Hard boil an egg in a cooking pot. Run the egg briefly under cold water. You want the egg to be cool enough to handle, but still be warm inside.
Peel off the shell and cut the warm egg into four sections.
Place the cut egg and the silver coin into a jar. Make sure the egg is still warm and that the coin isn't touching the egg.
Close the jar with the egg and coin inside. The sulfur from the egg yolk will tarnish the coin.
Leave the coin and egg inside the jar until the coin darkens to the color you desire. This may take several hours or you may even need to leave it overnight.
When the egg cools in the jar, you can remove it and warm it up again in the microwave. Warm eggs work better for tarnishing silver than cool eggs. You can warm up the egg as many times as you like. If the coin doesn't tarnish to the color you desire, repeat the process.