Stamp with StazOn ink. The sheet on the left is brass, the sheet on the right is copper.
Below is another project I did - a mini book inspired by Janet Loomis in the Spring issue of Belle Armoire Jewelry.
I found it's not easy to stamp on metal, it's very slippery. They have this product called StazOn remover that easily removes your image, which I must have done about 6 times before I got a clean image. And working with the ferric chloride is kinda scary - something that can eat away at metal is strong stuff, but it works! I like working with small pieces the best.