The next time I do a metal clay piece I will work on a Tutorial.
As far as the technique involved here, it was relatively simple. If you own a large flat Rubber stamp like Cool Tools creates you are halfway there. Oil with olive oil, then with a soft paintbrush apply silver clay paste in layers, allowing each layer to dry before applying another. Build up to roughly 4-5 thick layers. Here's the tricky part - getting that imprinted dried clay slip off the rubber stamp. Even with a well oiled stamp it can still stick. I discovered if I rub onto the back, a piece of clear packing tape it helps the piece stick together with minimal cracking as I peel the stamp gently away from the clay. Once the piece is off the stamp I trim the edges of the tape to match the shape of the piece and I leave that tape in place - it fires off in the kiln. If the piece has a few cracks I thin out some clay paste to the consistency of milk and gently apply it to the cracked areas and allow it to dry.
Tips: To create a worn look on the stamped pieces as if it had been in the ground for hundreds of years, I actually put air bubbles into the first layer of metal clay paste slip on purpose. The resulting surface is pitted and dented, and even sometimes warped, once antiqued it looks like something that is a bit cleaned up after it has come out of the ground.
Fire the stamped piece tape side up in the kiln. Firing it tape side down can cause to much heat under the clay as you fire the piece as the tape burns off and can actually start melting your clay! So tape side up!