Do not use flux since the purpose of this step is to create a layer of copper oxide. The metal will be a uniform dark gray. After rinsing, heat as before to the same temperature, this time for at least 10 minutes. The sheet should be only slightly gray. Pickle as before.
Reticulation is done with a torch.
Since it is necessary to make the metal molten throughout its interior, it is wise to either preheat the soldering block and then allow the heat to rise up into the sheet, or to work on a wire mesh. The sheet is brought to red with a sharp hot flame. The torch is quickly passed over an area allowing it to cool intermittently. The cooling is what causes the metal to buckle. The skin may melt and crawl without damaging the results, but this should be minimized since this flowing softens the sharpness of the ridges and diminishes the effect.