Hey Falanx

You are dead right - Kecap as salt bridge works really well (if you don't mind the mess).

I cleaned a chunk of 6Al4V I had sitting around and a piece of ordinary Al, each with the Norton Abrasive pad I use to give a brushed finish to Ti frames.

The PD measured with the Kecap salt bridge is 265 mV. This is over 90% of theoretical value, which is pretty good. On the run before I took the phot I got 280 mV which is even better. If you press too hard with the probes the metal surfaces contact and the PD drops to zero. It might be worth trying a piece of tissue paper soaked in Kecap, should eb more stable (and less messy).

I recleaned the surfaces and tried to directly measure contact potential. The PD with direct contact of two clean surfaces is less than the resolution of the instrument (0.1 mV).