Ferrous metals need to cool very, very slowly to anneal. Common nonferrous metals anneal just fine with a quench in water.
For larger parts, mix up a carburizing flame on an oxy-acetylene torch, then coat the sheet in soot. Open up the oxy to make a neutral flame. Heat the part, from a distance that won't melt the metal, from the back side until the soot burns off. Quench in water. Your metal will now be dead soft. Or, use a Sharpie and burn it off from the back side with a propane torch..........works well for aluminum, but you might not be able to exceed the heat dissipating capabilities of large, thick pieces of copper or brass with a propane torch.
Photoetch size parts can be annealed with a Bic lighter. BUT, those tiny pieces are easy to burn up too. Keep your distance and heat slowly for best results.