nothing to contaminate the silver. a little can go a long way in the electroysis process. we dont want to make silver compounds of any kind. that is why very pure distilled water is called for. using sodium in the water has turned people blue when they drank enough of it!
the silver doesnt have to be shiny. it just has to be pure and uncontaminated on the surface.
i have ruined several collctors coins using baking soda to clean them. coins are not to be cleaned. silverware and jewelry can be cleaned.