The Procedure
Because the process depends on localized heating it must be done with a torch, preferably one with a small hot flame. In the case of copper and brass an oxy-acetylene welding torch might be needed. The metal is placed on a clean soldering block, fluxed, and preheated overall. The flame is them played on the area to be joined or textured, typically with a gentle back and forth motion. The metal is brought through red to the flash point; the moment when the surface becomes fluid and shiny. At that moment the torch is abruptly taken away. This instant chilling causes the metal to contract and draw itself up into ridges.