She says that when the steel sheet begins to get a shiny look on the worked surface, it indicates enough strain hardening is set up in the metal and it s time to cease working it before rupture occurs. The pitch is then melted out in preparation for annealing the piece for further working. The pitch is a combination of pine rosin, fat or vegetable oils, and fine grain dirt mixed together, and it has to be of the correct consistency to perform well. The metal is first bulged out with a hammer on the end of a wooden stump that has a depression burned into the end. The pitch is heated with a propane torch to make it viscous enough to flow into the back hollow of the bulged-out metal cavity.
Some people refer to the surface work as embossing.
The pitch acts as a cushion that dampens the force of the tools and allows the metal to be bent and pushed at specifically controlled locations. The ends of the tools are tapered to fine, chisel-like points, but are not finished to a cutting edge since they are used to move and bend the metal against the undercoating of pitch instead of cutting through. The pitch can be melted out of the work and reused over and over as the need to anneal arises from time to time. Lead is stiffer and therefore can take a harder lick. She adds vegetable oil to the pitch from time to time to replace the oil that volatizes out of the compound when it is heated.