I got my hands on some patterned hammers recently and have started playing with them. Each hammer has two faces with different patterns. I bought one from Beaducation and the other at a show.
I textured some copper washers that I bought from Harbor Freight. The washers don't have a huge surface area and so don't show large area of pattern, but they are inexpensive to practice on.
Right away I whacked my finger. OUCH! I was bleeding. Maybe tomorrow I will have a patterned bruise. Just kidding--sort of.
These were my favorite two patterns. The one on the left is made with the square faced pattern and the one on the right is made with the hammer face with the narrowest lines.
I couldn't get a good picture of the other patterns. After my initial experiments I worked with the wide-striped hammer some more and got a much better looking pattern with it. The circle pattern hammer makes marks kind of like water and is pretty cool.
I could tell that if I hammered for extended periods of time this would aggravate my carpal tunnel. I get much less vibration in one hand if I use a tool to hold the washer in place. (Plus my fingers are out of range of the hammer.)
Most of these pieces will end up in earrings or bracelets. I textured both sides of the washers, although one side gets flattened a little when you textured the reverse.
Next on my list of metal work is stamping words on metal and etching copper.