Della Terra Studios makes some very high quality, high carbon chasing tools.
The texture of the business end of the chasing tool will be transferred to the surface of the metal. Smooth faced tools like these are often used to move the metal into shape. Chasing tools with textured faces can produce different surface effects and are often used in the refinement stages of repousse work.
Repousse and chasing are commonly performed over pitch. Pitch is a resinous tar-like substance which is semi-fluid when hot and hard when cold. It provides a backing for forming the metal that supports it yet allows it to be deformed. The pitch holds the metal in place during hammering and prevents the material from being pushed around, other than what is directly under the chasing tool. The pitch is used at different temperatures depending on the amount or depth of forming required. The final stages of refinement, called planishing, are typical done on cold, hard pitch. Soft pitch has the resistance of wet clay if you were to press something into it - Not your finger! Pitch burns can be very severe and painful. A good source for pitch is Northwest Pitchworks.
This is the lid to a box that I formed in the pitch bowl. I worked the metal from the front and back sides of the design by flipping it over in the pitch multiple times. Repousse refers to pushing the metal out from the back side of the piece - chasing is pushing the metal down from the front. There is a lot of back and forth between repousse and chasing when creating a relief. As the metal is moved around it becomes stiff, or work hardened. The metal will crack if the stresses are not relieved. Think of bending a paper clip back and forth until it snaps. The metal can be returned to it's soft, malleable state by heating it to very high temperatures. This process is called annealing. Annealing temperatures are different for each metal and alloy but generally occur when the metal is red hot. Some metals must cool down slowly after annealing but copper and other non-ferrous metals can be quenched in water for a quick cool down.
Here is a sample I did for a client a few years back. The fingers and details were created with repousse and chasing, and then the metal was bent up into the cupped shape.
I do a lot of my repousse work with the aid of a hand held pneumatic hammer. This is an air chisel with adjustable speeds. The chisel tools have been modified by grinding, forging, and welding. The tools are just bigger versions of my chasing tools. The air hammer moves the metal quickly and with pretty uniform results. Saves lots of wear and tear on the hammering arm as well!
Here are some pieces that I formed with the pneumatic hammer.
Statue of Liberty, Portlandia, and King Tut's burial mask. I have lots more to say on the subject of repousse and chasing. I will be posting step by step images of the techniques soon.