My understanding is that if the cathode is the same metal as the anode in the appropriate electrolyte eg brass or copper-brass or copper and copper sulphate solution, then you can re-use the solution indefinitely as the copper ions are being replaced. I just used a chrome oven shelf so eventually I'll need to replace the solution but I didn't have to worry about silver solder. I think lead solder contaminates the solution somehow.I don't really know a great deal about it. Also, for best results, the cathode should be slightly smaller than the anode. My set-up was the same as the picture except for the power supply. I stuck #2 to the panel with school book contact. Sticky cheap plastic stuff. Because it's a direct electrical process you don't need to worry to much about the back, as long as there's a electrical contact. The position of the cathode in solution is not important. Only the distance to the anode plays a part as to resistance etc. You can etch vertically.If your power supply is being over worked you can weaken your solution with water.