I have hand stamped a heart around the year on the 1983 penny and "40 & Fabulous" along the bottom edge of the back aluminum piece.
Aluminum will not tarnish or change colors and has a lighter weight than stainless steel. I use real coins in all my pieces so they will tarnish over time as any coins would do.
*Due to the hand stamped nature of each piece, being stamped one-letter-at-a-time, there may be slight differences in letter placement and spacing. This is not to be considered a defect. The differences are what gives the unique character to each piece.*