The reducing process will work with any and all low voltage ionic silver solutions. Furthermore, other agents that are known to work are; glucose, fructose, corn syrup, invert sugar, maltodextrin, honey, and cinnamon. Additionally, heating your Colloidal Silver will making it also acts as a reducer.
That being said, I've found that metallic or true Colloidal Silver is less effective than mixed or ionic solutions in certain cases. ie. I've taken up to 10oz of metallic silver daily to stave the effects of a bone infection with limited success whereas I found complete relief using 6oz of mixed CS. That was a solution I made using only heat during the process.