i am/was still generally interested on why such a question came to mind. but, to blindly answer your question, here goes. in order to keep your cell producing a pure product, you have to use materials that will not want to go into solution while you are refining you desired element. in order to dissolve silver and pass silver ions through your electrolyte, people generally use silver nitrate. this is pure silver dissolved in nitric acid. that same electrolyte solution will want to dissolve the metals that could contaminate it. any equipment used in your cell must be able to withstand the electrolyte, while the process is running. brass will dissolve in a silver electrolyte, as it contains mostly copper and some zinc (depending upon the alloy of brass). in fact, zinc will react violently with silver nitrate, depending upon how warm your solution is. i'm not sure how violenly the brass will react as an alloy, but i'm sure it will go into solution, and eat up any free nitrate while precipitating out any/all silver in said solution. you see, anything below silver on the reactivity series of metals will contaminate your electrolyte, and when your electrolyte reaches a particular level of contamination, it will begin contaminating your finished product. these metals would include copper, zine, iron, etc. this is why nick was ensuring that your SS bowl is non-magnetic, as it would contain too much iron and would allow it to give up iron ions and contaminate your finished product. a non-magentic stainless steel will not give up those iron ions, as they are bonded with the other ingredients of the stainless alloy. you could use pure gold, or PGM metals, or titanium for you cathode, but dollar for dollar, non-magnetic stainless steel is the most economical way of holding the electrolyte, being an electrode to pass electrical current and silver ions, while not dissolving/contaminating into your electrolyte. please take a little time to familiarize yourself with the reactivity series of metals. the first i was introduced to it, was a video of waste solution disposal from sreetips. he is very good at explaining the broad strokes of chemistry. i hope this helps.
