While browsing the web at lunchtime, I found references to this article about constructing a reference electrode out of a used felt-tip pen. So I tracked down the article tonight and have posted it at the link below. The electrode described is for Ag/AgCl, but it seems like the basic design could be adapted by using KBr instead of KCl.
Any thoughts on it's usefulness for measuring vAg or at least pAg? The more I read I see how knowing vAg or pAg is important for making more advanced emulsions so it seems like finding an economical solution for the probes would be useful.